hmm, volt modding seems a bit complex for the 9800gtx but you can hit like 900MHZ and above. on the stock cooling mine never hits above 55C so it stays pretty cool.
My 9600GT with the G94 chipset was a nice overclocker, I was pushing around 838 MHz on the core before I noticed artifacts at 840 MHz, and on the stock cooler and off of the reference card card at 650 MHz factory, mine was a piece from the good batch , I'd love to see what i could push with water cooling on it..... hmm
also, for some reason (it may be a misread but it seems my shaders on my 9800 GT are magnificent (check the middle # in my sig)
hmm well I wasn't sure, just not to keen on what exactly would be high for shader clocks, nowadays most people just look at how many shaders there are, and I didn't push with the shaders at all they just adjusted to the DDR3 speeds, maybe I can push them a bit further
yeh, I was gonna go for the BE 9800gtx+ but then the 4850 hit the market and I decided to stand back and wait with my 9800 GT in hand. anyways sorry I'm not trying to hijack the thread, with that said I'd say he could see a nice increase with the 9800GTX and like you said