How to decide on a Video card(s) for 3 monitors

[POLOgt]

Background:
I have one ACD 30" and two 20" displays (1 is ACD and 1 is Dell)
I am using two ATI 2600 HD video cards. They are both working very well, but now that I am running Solid Edge under Parallels.

I have one card running the 30" and the second card running the two 20" screens.
I will keep the 30" dedicated to one video card, and the maximum I will upgrade my two other screens is to replace my dell 20" to a ACD 23" which will leave me with a 2600 running a 20" and 23" for support files.

Now:
(I really tried googling a result, but nothing I thought answered my questions)
I am getting "lag" with the visual rendering of Solid Edge within Parallels, I believe I need a better video card to compensate for addition rendering.

I only run Parallels on the 30" and really am trying to decide what to upgrade to, or even if it will make that much of a difference???...

I have been serious about considering buying a FX5600 to run the 30" and use a 2600 for the two 20" monitors (possibly upgrading one to an ACD 23")


Bottom Line:
I just don't know or can not find enough information to know what combination will benefit me the most for the performance I wish for.

Any help from users with similar setups would be greatly appreciated,
I just don't understand enough about Apple's Mac Pro architecture to know what to do.

Notes:
I wish to continue to run in parallels, to use OSX for all my other applications I have to run.

 

[Chaos123x]

hmm have you tried VmWare Fusion to run windows instead?

I think it has better GPU performance. (not sure though)

 

[POLOgt]

hmm have you tried VmWare Fusion to run windows instead?

I think it has better GPU performance. (not sure though)

I have not,
Majority of the reason is because I bought Parallels...

I would consider that,
Will the 2600 still be able to keep up or should I grab at least an 8800 GT for the 30"?

Thanks,