Buying a used Mac Pro advice…

I am in the market for a used Mac Pro that will not cost me over $1,500. I need to make sure the Mac Pro I buy can run FCPX 10.1, Motion 5, Premiere Pro CC and After Effects CC without a problem. What I use now is the Mac Pro 1,1 (2 x 2.66, 16GB ram, ATI 5770) with a CalDigit VR. It's a dog! It just can't keep up anymore. Plus I can't upgrade the OS after Lion.

The Mac Pro 4,1 and 5,1 seem to be in my price range. I'm looking at the ones with the Quad Core processors "eight core" Mac Pro's. Seems to be a bunch of Eight Core 2.4 and 2.66 machines for sale. I'm thinking I could move my HD's and everything installed in the PCI slots from my old unit to the new used one. And not a problem if I have to buy new ram.

Does anybody have any experience with the for-mention Mac Pros, and how well do they run the for-mention software?

Thanks,

-Russ