Most GPU an i7 920 @ 3.3ghz can handle.

Solution
You will probably be fine up to a gtx 970... or maybe a 780 ti . Only though if you are able to overclock your cpu and quite a bit for that matter aim for at least 3.8 Ghz

Edit: Probably aim for 4 Ghz to be safe

Golfis

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Aug 31, 2013
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You will probably be fine up to a gtx 970... or maybe a 780 ti . Only though if you are able to overclock your cpu and quite a bit for that matter aim for at least 3.8 Ghz

Edit: Probably aim for 4 Ghz to be safe
 
Solution
The overall system is important. Having said that, the i7 920 is still very capable, and would not hold back any GPU to any noticeable degree. Sure, if you are benchmarking and comparing numbers, you'll see a difference in charts. However, assuming the rest of the system is up to snuff, you won't really notice sitting right in front of it and actually using it.

Shooting for an overclock to 4Ghz is a good idea as Golfis mentioned.