I sprint up to around 1000W (powertap/SRM) on 4.5's with a headwind fan, I think the rollers could go higher than that but my sprinting form limits me right now in that I don't want to break my neck trying to go higher!
As designed you can't adjust the Headwind while on the bike, but I have never wanted too, in fact I played with the positions, found the one I found most road like in feel and used tape to fix the position so it would be the same all the time. I don't think it would be that hard to affix a dowel or something similar to the headwind fan though so that you could make adjustments if you wanted.
Noise wise, I think its fine, on par with a lot of turbos. I watch cycling videos or cycling.tv while I ride and I turn them up a bit and it works fine. I close the door to my office and haven't woken up the kids or hear complaints from the wife, and believe me she would say something if it bothered her.
I wouldn't call myself a hammerhead but can't see myself needing more resistance than the 4.5's and the fan give me. I don't really ever adjust it either, I have the resistance on the fan set near the lowest and using my gearing normally I have the range I am looking for from recovery up to sprinting.
I have never owned/ridden 3.0's but I had the smaller 2.25's (?) and I didn't like them. The resistance of the smaller rollers makes it hard to just spin and the smaller rollers require a bit more concentration to ride so that starts to limit what I can do at high speed. On 4.5's I have gotten to where high speeds are still plenty controllable.
I don't know that one is louder than the other, I also have always had the all alloy rollers. My reasoning is that the higher mass should give you more inertia, ie more lifelike spin down if you stop pedaling. How important this is, or if I would like the plastic caps, I don't know but I do love the feel of the all alloy rollers.
Very happy though with my 4.5's and headwind fan, haven't been on a stationary since and by adding in a powermeter, I can't see me wanting anything more for indoor training.