I'm in pretty much the same situation as mr_phoenyxx myself...

I run two machines-

An FX8230 with a GTX1060 6gb and 32gb (4x8gb) main ram that I call Sarah

A Ryzen7 2700 with a GTX 1080ti 11gb and 32gb (2x16gb) main ram which I call Amber.

Amber was built to replace Sarah and her lengthy render times... (oh the irony)

Both machines are running Windows 7x64 Ultimate Sp1.

Sarah is running Poser 11.2.276. Amber is on 11.2.307

Both machines have the graphic card in the first PCIe x16 slot.

Just going by the numbers, Sarah's 1280 CUDA cores shouldnt be a challenge for Amber's 3584.

I've just downloaded the test scene that Ghostship2 has linked, here are my GPU superfly render times -

Sarah : 2131 seconds ( 35.5 minutes) using 1403mb rendering memory on device GeForce GTX 1060 6GB

Amber : 7140 seconds (119.0 minutes) using 1403mb rendering memory on device GeForce GTX 1080 Ti