What Hardware upgrade would increase ZBrush performance?

[system]

Considering that ZBrush is a native 32bit program Im assuming that cranking RAM above 8GB wont help any (though lower CAS couldnt hurt), Im wondering if a GPU or CPU upgrade would help the most.

Currently Im running a measly GTX 550TI as my graphics, Im thinking about moving up to a GTX 680, Im also currently running a AMD Phenom II x6 for my CPU. Though I know moving up to a nice i7 Sandy Bridge-E would be optimal, I dont really want to have to go out and by a thousand dollar processor with a $300 mobo if a $500 GPU would give me a considerable bump.

Just looking for opinions here.

[Gordon_Robb]

Afaik, at the moment, graphics card makes no difference. Faster processor and RAM is what you want. You do want over 4 gig though as only when you ave more than 4, will 4 be available for ZB to use. Also, there is a suggestion that ZB5 may be 64 bit.