After reading some reviews I think you're right there tbh, SLI on 775 just isn't very good.
And yeah, you kinda remembered rightly . I bought a 4890 just before I got my GTX275 and it was just crap, the fan had to spin rapidly to keep the card cool and it barely even overclocked at all. Always had a good experience with NVIDIA cards so I might as well stick to what I know .
Unless the price is right of course, then I might consider one of the 68xx/69xx series cards. Got a couple of weeks yet before this money's through so we'll soon see .