Well, there is a Technical board under Development that would be the usual place, found here - http://boards.cityofheroes.com/forumdisplay.php?f=578 - I'd suggest looking through there, there are a number of similar threads and also one from the devs themselves with suggestions.
I can see why you posted here though, so no harm done. 
My two cents? Wait until GR hits before making a decision. We have no idea how much more stressful on the system the new zones and updates will be. Imagine if you upgraded to a 5770 now, a month passes, and you then find out you should've gone even higher...? 
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"Hard pressed on my right. My centre is yielding. Impossible to manoeuvre. Situation excellent. I am attacking." - General Ferdinand Foch
Very soon I am going video card shopping and I am wondering what I should upgrade myself to. Here are my PC specs:
Operating System: Windows 7 Home Premium 64-bit (6.1, Build 7600) (7600.win7_gdr.100226-1909)
Language: English (Regional Setting: English)
System Manufacturer: Gateway
System Model: DX4300
BIOS: Default System BIOS
Processor: AMD Phenom(tm) 9750 Quad-Core Processor (4 CPUs), ~2.4GHz
Memory: 8192MB RAM
Available OS Memory: 7936MB RAM
Page File: 2173MB used, 13695MB available
Windows Dir: C:\Windows
DirectX Version: DirectX 11
Also the video card I am currently using is a ATI Radeon HD 4650. I have upgraded my power supply to 550 watt to allow for better performance. I am looking at something like a ATI Radeon HD 5770 because I heard it is a pretty decent card, but so far I haven't had too many problems running Ultra Mode with the 4650. However, I don't know what Ultra Mode looks like on anything better. I am worried about using Nvidia because I have no experience with them, but if the pros outweigh the cons I will give it a shot.
Also, this is the correct place for this question right? I am new to posting on the forums!