riMac 27" with dual SST 4K monitor (Dell 2415Q) @ 60Hz

[ronjns]

From reading threads in this forum I understand it's not possible to run dual 4K MST (i.e. Dell 2414Q) monitors both at 60Hz due to Thunderbolt bandwidth limitation.

But how about dual SST 4K monitors, will it work with riMac 27" @ 60Hz? The closest information I can get is from this thread:
https://discussions.apple.com/thread/6868583

The gent says he's able to do it with his rMBP 13". Has anyone tried with riMac? Advice appreciated.

 

[dagamer34]

I don't think he ever says whether the built-in display remains on or not...

Perhaps my biggest worry is Mission Control because involves the entire screen of all displays animating at once with transparencies and blurs. I've never seen it run at what I feel is 60Hz 100% of the time on any Retina Mac. It definitely feels more like a software issue than a hardware one. If a 6100 GPU can run even a single 4K display plus internal monitor, a R9 295MX with 4x GFLOPS and 4GB GDDR5 should be able to run a few.