New Mac purchase dilemma

I’ve recently purchase an upgrade to V6 and ordered a new Mac mini (I’m currently using V5 on an older Mac mini) which is now trapped (on its way to) at an Apple store where I’d arranged to pick it up. Apple are unable to redirect it to my home, and can only offer to cancel the order and start again.

So I was wondering if I was to purchase a used Mac Pro (round can type) with the D300 graphics cards, would this make sense? It’s about the same as the mini in terms of cost and processing speed (6 core 3.5Ghz) but would have a couple of graphics cards.

Plus, I’m assuming that I would be able to run windows on the same machine and take advantage of the multiple processors (the windows hardware spec mentions up to 64 processors, so I’m assuming it runs them, but I believe the Mac version of Rhino can’t take advantage of multiple processors).

In truth I’m confused by the whole thing, and at the moment want to ignore the new license (the V6 WIP ran slowly on my current machine) and just stick with my current hardware and V5, it works.