Some good news is that I've just tried running the test scene with the demo of Poser 12 and the 1080ti slowdown seems to be fixed. Also, the Optix mode for RTX cards is a LOT faster. Speeds seems to be faster across the board. The bad news is that at the present time, you can't use more than one card to render. Here are the results:

Downloaded Test Scene Poser 11.3 RTX 2080ti 622.54 Seconds

GTX 1080Ti 6600.24 Seconds

RTX 2080ti+GTX 1080Ti 373.8 Seconds

Downloaded Test Scene Poser 12 RTX 2080ti 475.13 seconds.

GTX 1080Ti 531.63 seconds

RTX 2080ti Optix 266.89 seconds.

i7 5960X, 32GB RAM, GTX 1080Ti, GTX 980 Ti, Windows 10 Professional.  Running Daz Studio 4.11, Poser 11, Vue Inf 7, Photoshop CS4