The difference in Ac 500 and less is ONLY the flow (and the size of course). Difference in a emp. 280 and a 400 is not ONLY the FLOW rate and the size, BUT 400 has an additional biowheel and double in size
I have used both filter floss, and tried that "cheap" trick of the nylon quilt batting you can get in the crafts department, both work great in those extra "user fillable" carts on my emp 400's.
I have never had any ammonia,nitrite or nitrate spikes by rinsing off my sponges or filter media in regular old clorinated tap water.The media isn't in the water long enough to kill off a significant amount of good bacteria.
I've always had bio-wheels.... They work for me and I like them! I have 2 Emperor 400's on my 125g now, and plan to get a 3rd one when the Top Fin 60 (freebie from uncle) that's on there now finally dies.
I really don't know why people say they're noisy. I can't hear either of mine at all. I can understand maybe hearing water splashing if you don't keep your tank really full, but I do, so I don't even hear water either.