According to the article, GTS 250 is ALWAYS faster than 9800GT at any resolution. See crysis page if you are interested in playing crysis. Its 37.1 vs.31 at 1024x768. You might want to check the data for 1280x1024 resolution as its the closest to 720p.
Personally, with an exception of crysis, I dont see any gain at buying 250 over 9800GT, as both can handle all t he games (except crysis) at more than 60FPS at the said resolution.