Processor Advice

Seeking opinion....just bought a Athlon64 4000+ from a guy who had it one month then decided to go with a dual core. It was such a good deal I could not pass it up. My question is that my current setup (A7N8X, XP 3200+, 2x512 XMS 3200, 9800-PRO AIW, 2x WD 800JB sata drives) is starting to bog down with AI, MegaScenery + City, and other freware scenery I have installed. I am considering purchasing the ASRock Dual-939 so I can hold on to the 9800 AIW a little while longer before plunging into the 7800 GT. Would keeping the same drives, memory, and video along with the new cpu and mobo result in faster smoother performance or is my bottleneck the current 9800 video card?thx