Well I tried the Heavy Round and after using the Elite Cav for so long, it's definitely noticeably slower, it slows down my feints by a lot, which I do not like, makes my pick a lot easier to track. And pulls block up noticeably slower as well, I think I might just loom Elite Cav, sure there's no speed gain, but it's still more speed then a loomed heavy round and that's all I need
Shield speed actually has no effect on feints. Your eyes are just playing tricks on you because of the different size of the shields. No matter what shield you use, the animation takes the same exact amount of time.
Shield speed just determines how fast a shield blocks after you hit the block button. A 100 speed shield is as fast as manual blocking. A slow shield doesn't block until sometime after the shield is fully raised. My guess is that shield speed represents a percentage based off of manual blocking speed. So a shield with 87 speed blocks 87% as fast as a manual block. Just to give a point of reference, with an 87 speed shield, 6 shield skill and 75 ping I can still block feints and chambers. Any slower than that and probably not.
If you're looking for a shield, there's many factors you have to think about.
Can you use it with a horse? - VERY important if you think you'll ever ride a horse with a shield.
How long will it last vs axes? How long vs swords?
How much does it weigh? - This is important for two reasons. A heavy shield will slow your movement more, but will reduce your chances of being block stunned. If I'm using an elite cav, there's a good chance someone with a bar mace will block stun me. Not so with my heavy round.
How's the coverage? - Much more important for melee than ranged.