You should... pound for pound .. in my limited opinion at least IL2 is still the absolute best bang for the buck you can get in decent simming.. Yup... it's dated... and yup..... there are things out there that do some thigs a lot better.. but nothing does everythiung that IL2 does the way it does it.. With CUP you can go from Flanders to Korea.. all in one package. Can't bet it with a stick...
If you are running PF 3.XX decently you should be ok. From what I gather there might be a 2-5 fps hit.. which isnt much..... If you do what Billfish said it will help tremendously. Do the dfrag and spyware scan on a regular basis too..it helps.