The 6850 is probably a bit stronger card than the rest.
But, any of them will be a bit better than your 9800GT.
The "OC" indicates an overclocked card. It will perform slightly better than a non overclocked card at the expense of higher temperatures.
If you are worried about heat, I would avoid them.
If you change from nvidia to amd, you will have to remove the nvidia graphics drivers and replace them with amd drivers.
sorry geofelt, but i want to know if the Nvidia cards are better in games or AMDs
because i heart that the AMD has some problems with games or some other issues i can't remember exactly
maybe these problems are for older cards because i heard this info along time ago
do you know which is better (gigabyte or sapphire)
and thanks for your replies