the raptors deffinatelly boost performance, but to really get an appropriate answer to your question, you must have a budget set out in advanced. If you don't have one, it is a little more difficult to say what you should do.
steer clear of asus s939 motherboards
Talking with experience, i would beg to differ. I have had nothing but success with my board after the first few errors were worked out (it was my first build). Also, not all asus A8N boards are alike. I believe there are two or three still being produced (premium, deluxe, and something else... normal?). Personally i have had NO issues at all with my mobo.. its held out great (no jumpers, no problems).
the x16/x16 is a TOTAL waist of money. you may see a 50 point jump in 3dmark06 at most, but really you cannot tell a single difference between a normal board and that asus one.
my 6800gt (oc'ed however - see specs in sig) can play bf2 at full settings without a problem. I've even tried chocking up the cpu by doing a virus scan at the same time with no problem of playing bf2... part of this could be due to my RAM i guess, but i wouldn't think so.
all together though, i think keeping what you have would be the best option (in terms of price
erformance ratio). but again, you have to really have a budget.