help with graphics cards, psu's and motherboards...

Hi everyone!
I have the following system:

LC POWER 550W SILENT GREEN POWER PCIe
ASUS P5B CHIPSET 965 SOCKET 775
CORE 2 DUO E6400 2.1GHZ
4 gb memory ddr2-800
Radeon HD 4850 512MB

And i wanted to upgrade the graphics card to either the [SIZE=12px][FONT=Verdana]HD 6850 1gb or the gtx 460 1gb..[/FONT][/SIZE]
[SIZE=12px][FONT=Verdana]The problem is that all the 6000s are all PCI-E 2.1 and they are known to have issues with PCI-E 1.x. Its not always the case, but there are some reports.. [/FONT][/SIZE][FONT=Verdana][SIZE=12px] i did some research and apearently its a hit and miss and is dependent on the motherboard… while 2.0 works perfectly.. s[/SIZE][/FONT][SIZE=12px][FONT=Verdana]o if go with the 6850 and risk it not working on the motherboard.. unless anybody ever tried a 2.1 graphics card on a P5B (P965)? Or any similar card? and could tell me if it works?[/FONT][/SIZE]

[SIZE=12px][FONT=Verdana]The problem with the gtx 460 is im not sure if the psu can handle it… any input in that would be apreciated..[/FONT][/SIZE]

[SIZE=12px][FONT=Verdana]A quick note, is that i have no intention of overclocking any of these components.[/FONT][/SIZE]
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