Every system is different.
5770s OC pretty nicely without needing modded cooling, so you could probably squeeze an extra 100-200mhz out of it (maybe even more). Work your way up slowly and see how far you can get without overheating/artifacts.
With your processor, it really just depends on the chip itself.
Those chips OC nicely though, so you can probably squeeze at least 100-200mhz out of those without needing better coolers as well.
Basically, just test smal increments and watch your temps. When they get outside the safe-zone for 24/7, stop and stick with what you have or look at better cooling.