The 5770 is faster than the 9800GTX, and considerably faster than a 9800GT.
Wanted more info, can't seem to get sites to do side by side. Just replaced the 5670 w/ 5770. My first build, msi X58 PRO-E, intel i7 920, 6gig osc 1333, etc. Kinda tricky, still blue screening occasionally.
Well, the 5670 ~= 9800GT, and the 5770 is significantly better than both. Toms Heirarchy list might help a bit as it shows the 5770 as 3 full tiers above the 5670 and 9800GT. Its a pretty huge jump and very noticeable. Don't know how much more detail you want other than true benchmark numbers, but its A LOT better. http://www.tomshardware.com/reviews/best-graphics-card,2569-6.html