Incorrect. You cannot log in using the workaround during downtime if you convert a web account to a Steam account. I know this personally.

Converting to Steam:-

Shouldn't convert because:

If you don't have a rather fast computer (with decent RAM and CPU speed), best not to convert. SK takes up enough CPU as it is.
Steam will ALWAYS have to be running in the background. If you have a fast machine, good then it won't really matter. But if you don't, best not to.

There is this thing called Steam overlay, which allows you to basically chat to your friends in the same window, and take screenshots to your profile, and it lags the whole thing even more. You DO have an option to turn it off, but then you can't enjoy the "benefits" of having it on.

You mentioned you like the mic feature. That is also one of the things that causes a lot of lag. Especially in Arenas with huge waves, and fire animations -_-.
If you live in one of them non-server areas, or usually get lag playing, don't convert.

Payment issues: If you convert to Steam, every time you buy anything in SK, you'll be taxed. Like a dollar for every 20 dollars maybe?
And also you need to enable Steam Overlay to be able to Checkout. Also take note to not be in a "restricted country" like I am because then you can't buy ANYTHING at all. (Wish I'd known that, forever without Elevator Pass, since you can't gift those)

Since you have to pay through Steam wallet, you need to charge it up in fixed amounts, like 5 10 20 dollars. So let's say you're getting the Ele pass.. you have to charge in 10 dollars.

Authentication issues: every once in a while, an update comes around that does not like Steam, or Steam does not like it. Either way, you can't log on, and forced downtime can be quite annoying. It can take anywhere from 1/2 a day to a week to resolve (rare, though I think they are occurring less and less now).

Should convert because:-
If you are f2p, you can get the DLC (but they said something about working to trade in-client)
Chat, though it contributes to the lag
Trade CE for other games
Take screenshots to upload immediately (and all in one place)
Never enter your password again! Slightly faster log-in I suppose.

TL;DR: if you are just going to use Steam to play ONLY SK, I suggest you do not convert. You could always get a steam account, add all your friends, and talk to them there if you really need the mic feature.

I also highly suggest that you get Steam, get SK, and then create a new character on that Steam account, run a few clockworks, check out its features, and see how well it works for you. If you decide you like it enough to convert your main char to it, then do it xD If not you can just delete it. xD

Also, Steam accounts come with limited features (such as not being able to add friends, though they can add you, or open multi-person chat group sessions) You either need to buy a game, or have someone gift you a game.

Since you have to pay through Steam wallet, you need to charge it up in fixed amounts, like 5 10 20 dollars. So let's say you're getting the Ele pass.. you have to charge in 10 dollars.

Not true. Steam Wallet has a minimum charge of $5, so if your cost is under that you MUST pay $5. If your charge is over $5 you have the option of charging that exact amount.