The GPUs out now are ridiculously more powerful. I said "~6 months or less" for new cards, but you could reasonably disregard the "or less" part of that. Your monitor must be at a low resolution for the 9800GT to be maxing things... or you're not playing anything too harsh. It is true that there is a big GPU bottleneck, performance could double or triple with a new enthusiast card now.
But since you seem content with what you're getting, wait... because it just means an even bigger performance jump around the end of the year.