If you have a spare nvidia card lying around, try the dedicated physics and see how that goes. If not, you could go on the cheap with something like this:http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=6460821&SRCCODE=LINKSHARE&cm_mmc_o=-ddCjC1bELltzywCjC-d2CjCdwwp&AffiliateID=Es5Ekr9eEBk-7Tz9Pj7KR2J44pHvIkkMsg
If that doesn't bode well, then I'd go for the 2nd 570.
If your trying to stay on the cheap, I'd recommend trying a cheap card and going from there. I agree with alyoshka, you will see a drop in fps with the physics card as I have read that to be the case in more than one instance.
I'd personally like to know what route you take and the results you get. Post back and update...