Experience with Radeon Pro 580 with 8GB video memory GPU in new 27-inch iMac?

Is anyone out there editing on a new 27-inch iMac withan AMD Radeon Pro 580 GPU?

I'm researching to upgrade an edit system. Going PC is not an option, and I am focused on finding a solid mac platform for HD and 4K editing.

While Apple is getting ready to release an iMac Pro and new Mac Pro later this year, no specs are available. The best stop gap measure I can come up with is to explore purchasing the currently available 27-inch iMac. Sadly, the GPU offering is not listed here: Adobe Premiere Pro System Requirements

Does anyone have personal experience with this GPU and Premiere?

Or Adobe can you chime in? Has this GPU undergone any performance testing?

Thanks!

Lindsay