i can live with a little more background noise, but i cant live with playing games on low res and still getting jerky frames.
The X1950pro will give you significantly better performance at 1280X1024, check toms charts if you don't believe me.
And as far as DX10 go's, all games for probably the next year will be both DX10 and DX9, and the 8600 wont hold up as a gaming card on DX10 or DX9, so i'd go with the X1950pro on good ol DX9 and actually be able to play and enjoy the game, instead of a silent 8600GT on DX10 where i cant keep track of whats happening in the game because it's coming at me like a slide show. Even on current games the X1950pro is a much better performer, on games like Prey, the 8600 will be unplayable and the X1950 will give you a great playing experience.
If you want to game, frames and graphics quality are all that matter.