I installed my Omniums today on my Felt TK2 replacing the stock Sugino 75s that came with it. I made almost a 100 dollar profit by doing this and I don't think it's a downgrade at all. From the short ride I did on them I couldn't really tell a noticeable difference stiffness wise, but I did notice that they were smoother than the SG75s. Also I finally have an almost silent drivetrain which I was never able to achieve with teh SG75s, but that doesn't really matter.
I'll be doing a longer ride tomorrow and I'll see how they feel. From what I read they get smoother after a certain break in period but so far I am pleased on how they feel.