Without a doubt, the 9800GT is the better option of the two. You shouldn't need to worry about the power consumption of the 9800GT either. Since it doesn't require a power connector, the most it could possibly use is 75W (from the slot). Your power supply should be able to handle that.
ATI will be announcing the DX11 cards for their lower segments at CES 2010 in January. No (solid) word on Nvidia yet though.
ATI will be announcing the DX11 cards for their lower segments at CES 2010 in January. No (solid) word on Nvidia yet though.