Ok thanks Orbital. I was feeling that the 5-7% posted above would kinda be enough of a dip to be noticable but according to the link posted it really isn't.
Also, I have a lot of ram so I would think that would help buffer from any issues, as well as having a lot of ram on the video cards themselves.
This is all good info to know if I ever do decide to go crossfire.
I guess the only thing that crossed my mind now is, with the 4870's, and soon the 4870X2s that'll end up in systems crossfired, how is the northbridges in todays systems handling all data being shoveled at it from so many sources. The ammount of data that a motherboard has to content with just keeps skyrocketing upwards faster and faster. I know the FSB speeds have gone up but it doesn't FEEL like its keeping up with the ammount of data we're sending at it.