Hi Basem, do you have a link to both so i can see which two your actually looking at, i'm a nvidia fan myself, but there all based around the same functions, and the most expensive is not always the best model, throw a link then i will check them out..  

As some of you know i'm working as a reseller so here are some infos:

The 850 XT is better then the 850 pro

The 850 series:
1.Radeon X850 XT-PE     
2.Radeon X850 XT    
3.Radeon X850 Pro    

The 850 pro usually has only 12 Parallel Pixel Pipelines
I think that's why the wrote on their website  "Up To 16 Parallel Pixel Pipelines" and not it has 16 Parallel Pixel Pipelines    
The 850 XT has 16 Parallel Pixel Pipelines a better  Fill Rate and can handle mor  Number of Polygons Per Second.
 
They also have usually the same  Clock Speed of Video Memory (520/540) but looks a bit strange on the website too
Only the 850 XT PE <-(platinum edition) has a faster Clock Speed of Video Memory (540/590)

But to be honest they are not really much faster then the 800 series.

The 800 Series:
1.Radeon X800 XT-PE    
2.Radeon X800 XT    
3.Radeon X800 XL
4.Radeon X800 Pro

If you can get a cheaper one from the 800 series you can save some money  

In some benchmark tests (Unreal Tournament 2004 1600x1200x32 4xFSAA 8xAF) the X800 XT-PE !!! was faster then the X850 XT-PE (but this shouldn't be after ATI's product name philosophie (but it is   )

Hope i could help ya

Alright guys, Thanks for all your help  
I am gona go with the 850XT
Now if you'll excuse me, I need to go out and find me a wife, got a few other things I need  

Thanks again fellas!

Basem