Mike. I wouldn’t concern yourself with the power if the M395X. I have a MacPro 6,1 with the (non-upgradable) D300. Rhino for Mac is workable. It’s not fast or even desirable because the D300 is a pitiful card. Now, had I known the video would have been poor, I would have bought one of the last remaining 5,1 MacPo machines that came with Radeon HD 5770. The card was a decent card, but I used a Radeon 660Ti which smoked the stock D300 of my new MacPro (go figure). The 660Ti was unstoppable and could handle anything I threw at it.
Now, my new MacPro has the D300, and according to many sources it’s comparable to the W7000 article. Performance specs on the W7000 can be found here: W7000 (4137)
The performance specs for the M395X are here:
However, I should note that the W7000 had twice the VRAM as in the MacPro. Bottom line, the graphic power that comes with the iMac you’re looking at will more than do.