Questions about Shields

1. I got an Avenger recently and the only thing I am not happy with is its abysmal speed. So I decided to buy a Swiftstrike Buckler recipe. Can you really notice the speed boost? Does it make a difference? And how does Swiftstrike cope with monsters (T2)? Especially Slimes and Constructs because I usually only do Jelly runs.
2. Shield health I take it, is the strength of the shield. Higher health means breaking after a longer time. So why does both of my Horned and Wise Owlite turn yellow when hit by a Lumber (those tree robots)? Wise Owlite has a far better health so it shouldn't turn yellow with just one strike.
3. And what about Shield status resists? Does it mean if I got a shock or fire, I take less damage if I use the shield?

But the Wise Owlite offers a far greater health (around 4 more bars), it shouldn't turn yellow that quickly. Are gears of higher tier completely nerfered to the level of the tier you are in or do they offer a little bit more than the gear of that tier?
When I am on fire and I use Horned Owlite, it still take around 1.5 bars of health off me.
There has been a lot of discussion in the past about the questions you're asking, and the generally accepted answers are this:
1. ASI is very helpful. One of the main ways it's helpful to me, personally, is not by allowing me to swing faster. Rather, it's helpful because it allows me to get my shield up faster following a combo. Even if you don't always notice the increase in speed, you're likely surviving a bit longer than you would have without it.
Swiftstrike is decent in tier 2, but I wouldn't use it beyond there unless you're pretty experienced.
2. Like Andrea said, higher * gear has reduced effectiveness in lower tiers. However, when I was experimenting with shield uv's, it seemed like the higher def shield was holding out longer in the red, rather than turning red more slowly. So perhaps your shield just needed more hits to prove its effectiveness?
3. Shield status resists do not reduce damage from the ailment, or reduce it's duration. Instead, a shield resistant to a certain ailment will lose less shield health when hit with an attack that can produce that ailment.
1) Yes. Speed boosts make huge differences. I'm using vog cub set with very high speed boost with wild hunting blade, and I daresay I'm the fastest attacking player in SK. swiftstrike kinda sucks, but it's ok for jelly runs.
2) That's because 5 star stuff are nerfed in tier 1 and 2 (it won't be fun if a divine avenger did 50000 damage to a jelly with 20 health in tier 1), so they basically have the same health in tier 2. The difference is highly noticeable in tier 3, however.
3) Yes. if you're on fire, you take almost no damage if you shield up with horned owlite shield.