I've built several like that in p180 cases, 830cpu, stock intel heatsink/fan, hdrives in lower section, passive vid card, gigabyte 855 boards.
Running 2 instances of cpuburn, they got to 57C and idled at 43C. I think that is pretty good for the stock cooler, but I attribute it all to the 180 case. It really seems to exhaust all the heat thru and out of the case.
I set them up with the top fan moved to the front upper intake and the top exhaust sealed off.
If you want a better cooler, I've used zalman 7700cu on prescotts with good success, but in the p180 case the stock setup was good enough.