Heh...you might want to move this to technical support...

By your post, it seems that you have HAD better performance, but are now having issues with it running slowly. You might want to turn off Anti-Aliasing and maybe lower the graphics quality.

As for why it's gone slower...what's your OS? I'm assuming your using Windows, because it's usually the culprit behind sluggishness.

Windows has notorious problems, many which are underlying and would take 5 or more paragraphs to explain. I need to ask, is your whole system slowing down? With Windows 7 and under (I can't say much about 8 yet...it's been too recent to see exactly how that plays out.), they will all inevitably slow down as they update and as the user(s) install more stuff on them. There are three ways to fix this which I can think of off the top of my head:

Reinstall Windows: Depending on your setup, this may or may not be easy. By reinstalling, you'll be deleting EVERYTHING on the partition. (read: hard drive unless you've partitioned your hard drive...I'm assuming you haven't.) Care should be taken if you chose to do this, and you will probably want to make a reliable backup somehow. (Burn CDs/DVDs, upload things you want to keep on a backup site, etc. Try Google if you want some ideas.) Keep in mind that you will lose your Windows settings if you do this, so any settings you set will have to be set again.

When backing stuff up, keep in mind that you don't want to back up everything, especially C:\WINDOWS and C:\Program Files. These are where the specific files for that Windows install are, and these are usually the things which slow it down are. I'm not saying you cannot back everything up, (if that makes any sense...) but just don't restore everything to exactly how it was...doing this will leave you back to square 1!

On a Spiral Knights note, although your controls and graphics options won't be kept if you do this, (unless you back that up, too!) your knight, along with his/her/its gear, achievements, crowns, CE, and everything you've worked/payed for will be kept no matter what you do to your computer.

Optimizing/Speeding up Windows: This is the grab bag of the trio I list here. It can vary from old program removal to overclocking, and from completely safe to hardware breaking. If your system permanently breaks from something here, it's your responsibility. I'm merely giving some options.

• Close any unnecessary background program, including the ones in the toolbar and minimized ones. Some large culprits are instant messengers, that joystick controller that came with your joystick but never use, and (almost always) a virus scanner. Scanners are one of the most resource consuming programs, and running them with games can cause issues. (At least activate, for example, the gamer mode that some popular scanners have.) If you've already done this, read on...
• Clean the registry by using Ccleaner. (the free version should be fine) It cleans up registry, which can get beyond dirty if Windows has been installed a year ago. The registry, in short, is a huge jumble of files which points all over your system. The registry is used at all times, from power on to power off. If it's cluttered, it will slow down your whole computer. This is probably the easiest and fastest way to speed up a system. I recommend it most.
• Uninstall anything you don't use via Start>>Control Panel>>Add or Remove Programs (or similar). This is a bit like the first one, but with will also save space on your hard drive. Unfortunately, I've found that uninstalling stuff doesn't always remove the registry entries which go with them, so running Ccleaner after uninstalling might be a good idea to ensure that there's not a trace of what you uninstalled.
• Entering the realm of dangerous, turn off Services which aren't needed. To turn off Services, go to Start>>Control Panel>>Administrative Tools>>Services. This will open up the Service Manager, where you can change what runs in the background and what is active from the second you load Windows up. By looking at the things here and their descriptions/names, you should be able to tell what you need and what you don't. You should Google for it if you aren't sure what you should do. Keep in mind that turning off some of these things could potentially break your computer, so you might want to make sure you know how to activate Safe Mode so you can recover from a mistake.
• Close unneeded processes. To do this, hit Ctrl+Alt+Del[ete] all at once, and you should get a task manager. Go to the Processes tab and end anything which you think you don't need. This is safer than turning off Services (see above) because things will always restore to how they were next time you turn on the computer. (So if it crashes, just reboot)
• Change what runs at boot time. This is as dangerous as turning off Services. (You can turn services off here, too, but it's more confusing.) Go to Start>>Run and type msconfig in the blank space and click OK. You'll end up with a delightful little System Configuration Utility. Go to the Startup tab. This doesn't make as much sense as the Services thing, so I won't blame you if you shy away from this. A few things I can say you can turn off would be anything that says "Printer" or "Adobe" because you won't be needing Adobe programs or to be printing things when playing SK.
• Lastly, this is the thing which I have no experience in and I highly recommend not doing this unless you have someone skilled helping you or you are willing to buy a new computer if things go wrong. This is known as overclocking your system, causing the CPU, RAM, GPU, etc. to run faster than it normally should. Depending on how much you overclock, you might need special hardware. This can increase the performance of your system, but, and here is the hitch, it can burnout or permanently damage your system if you do it wrong. Once again, I highly recommend against doing it unless you are desperate and/or you are extremely interested at becoming skilled are already skilled in doing it.

And finally, find some way to check for viruses such as ESET. Viruses can slow a system dramatically as well as make the system insecure. Just keep in mind that running ESET or another virus scanner can slow down the system, too, because scanners tend to be resource consuming. Just make sure you disable/turn off the scanner after it does its thing.

Now, time for me to cross my fingers and hope that you are using a Windows system and all this stuff I've typed isn't for naught. Good luck! (But don't shake my hand....I want to keep my hand in an "unbroken" state....)