Power Supply enough?

That's actually a very good power supply and it has more than enough power for your 8800GT.
Another option is the Corsair 400CX 30amps +12V power and $50 with free shipping and $20 rebate.

Not that it matters to you but the combined +12V amps for that PSU is 30, not 34. From the data label you see it has a max combined wattage of 360 which gives 30amps. (360 watts divided by 12 volts = 30 amps)
17-151-076-S05
 
OK; I see you actually already have the Seasonic.

You didnt mention what else you're going to be powering with the PSU but it's likely you'll be in the 200watts of power range for the whole system and you'll be in good shape.
Here is an OC'd Core 2 Duo E8400 @ 3.6 GHz system.
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