I jumped to the V-Ray GPU train now and it’s quite good working. I use two 2080ti and one 1080ti (per extension cable). Best it works if the 2080ti are used for rendering only and all other software is set to the 1080ti in the Nvidia control panel (it’s only Photoshop and Rhino which are set to the 1080ti and the monitor is pluged to 1080ti too). Also Enscape can be set to still use one of the 2080ti.
My goal was to use the 2080ti in NVlink mode to get 22GB VRAM, but it’s not working yet. I’m waiting for a feedback from the developing team, since it should work. But without NVlink more speed is available and my setup allow to use approx. 11GB for rendering only, so quite complex scenes can be rendered.
Cost/Performance - I use my old DualXeon and upgraded the cards only, so for me it was the best cost/performance way. Also I like the GPU upgrade way, the system (CPU/RAM/OS) can stay untouched, you only need to change cards.
I would look for a good Threadripper (1950X or 2950x) PC and start with a 2080ti and a smaller GPU for monitor use. Later, I would add a second 2080ti.
GPU rendering - it works best per LC+BF and this is slower than my LC+IM setup used the last past years. But the V-Ray next and GPU bring back the old speed, but with a great stable quality - fine details and no splotches anymore. My impression is my DualXeon (32x3.2GHz) in LC+IM was so fast like one 2080ti LC+BF now.
V-Ray next - for me it has started to be stable enough since the VfR next release. There are some limits and bugs, but I hope, the next months will stabilize it. I hope the speed will increase, if the RTX features are more supported.