Geia sou Dolphin,
I have (had) IL2 running on machines with ATI9800, NV6800, NV7800, NV7900SLI, NV7950GX2(SLI), ATI1950...
Answer #1: Buy an ATI card
Not being funny, ATIs quality of picture is better and allows to distinguish better.
Answer #2: Do NOT buy a 7800 or 7900 series card
They are fast but, the quality of picture is a lot worse than your 6800, you will be surprised...
I was told the 8800 series have a much better picture quality than the older series - did not have the time to test yet...
Answer #3
Human eye can identify "movement" ten times better than distinguishing the shape of a static object (do not nail me about the ten factor, it is long ago I watched Discovery channel...). So, it comes down to how clear can you identify small moving objects subsequently how well your card shows that.
For this reason you need to test the following:
a.) conf.ini (always make a backup)
Get all Nividia Optimisations out ! In the OpenGl area, everything that ends with xxxxNV=1 is an optimisation for an NVIDIA card. Put this back to 0
b.) graphics drivers: Some drivers are better than others. Unfortunately it is very time consuming re-installing drivers. The NGO drivers are supposed to be very good (at least I confirm this for my 7900GTX SLI).
CAREFULL: You have a risk turning off all optimisations: Your 6800 is a very good card (still) but it may not have enough power at the end to let you enjoy a stutter free game.
Hope it helps,
~S~
Manos