I would think that would be the case yes. It depends a bit on the rest of your system though. Most Reviews are done with i7 CPU's these days and typically at your resolution a 5850 would get around 8-10 extra FPS which would be approx 40 ish instead of 30 ish running Crysis. That would be running on enthusiast settings with some AA, it varies between reviews some use 2x some use 4x.
So unless you also have an i7 which, not being funny but i doubt it given your res then you can expect to be a bit lower.
Its possible that your CPU could hold back anything faster than a 5770 anyway.
At your resolution i would think the AA at X2/X4 and high settings would be achievable, you can post the rest of the system if your curious about your CPU and if it will be ok should you decide on a better card.
Mactronix