Hey everyone, Mark tossed me an email earlier to let me know about this thread. I think I can throw some light on things here! Sorry if I miss any details, I skimmed through the thread, but may have missed something.
In terms of raw performance, the RTX 2080 Ti and Titan RTX are pretty much identical in Resolve. This article has the latest public results if you want to dig into it: ww.pugetsystems.com/labs/articles/DaVinci-Resolve-15-NVIDIA-Titan-RTX-Performance-1328/#IstheNVIDIATitanRTX24GBGPUgoodforDaVinciResolve? . I'm also working on updating our benchmarks and re-did testing with Resolve 16 Beta and the results were pretty much the same - so nothing has changed in the newer versions.
If you are looking for the most performance, dual RTX 2080 Ti is generally going to be faster in Resolve than a single Titan RTX. This has the latest benchmarks looking at GPU scaling in Resolve: ww.pugetsystems.com/labs/articles/DaVinci-Resolve-15-NVIDIA-GeForce-RTX-2080-2080-Ti-Performance-1238/#GPUScaling-BenchmarkAnalysis , but I would expect dual RTX 2080 Ti to be up to about 20-30% faster than a single Titan RTX.
The exception to this is if you actually need the extra VRAM that is on the Titan RTX. This is a weird coincidence, but I was actually just looking at VRAM usage the other day while working on our new benchmark and stuck a quick chart up on Twitter: twitter.com/PugetMattBach/status/1143309444417110016
VRAM usage is a bit weird (just like system RAM) since there is some factor of "expand into the usable space", but the 11GB on the 2080 Ti should be just fine for anyone working with 4K media and timelines (or even 8K media in 4K timelines). The 2080 Ti is our go-to card for Resolve, and it is rare anyone has issues with the VRAM with 4K media unless they are using extra plugins that eat of VRAM. The 24GB of VRAM on the Titan RTX is really only going to be useful if you are going to work with 6K/8K media. Without that extra VRAM in that case, working in the edit/color tabs isn't going to be feasible unless you really like seeing that "out of memory" error pop up.
A couple other things to keep in mind: First, there are no "blower-style" Titan RTX cards, so the most you can put in a workstation (unless you go to extremes in terms of airflow) is going to be 2 cards. The 2080 Ti, on the other hand, we regularly use up to 4 cards in a single system. Useful if you might want to expand later.
Second, Resolve doesn't use NVLINK yet, but if/when they do, that should make dual RTX 2080 Ti even faster than a single RTX Titan. Depending on how they implement it, it may also mean we will get to "pool" together the VRAM from both the cards. I give that a 50/50 chance though, it is just as likely they focus on NVLINK for pure performance or ignore it completely.
Hope that helps answer your question! Basically, for you, get dual RTX 2080 Ti.
By the way, someone mentioned needing a US IP to register a full account at Puget Systems. That is true, but we did just add social media login that doesn't care where you are from. We also have open comments on all our articles and contact info on our About Us -> Contact Us page. Neither of those are behind a registration wall (although you need a Disqus account to post comments I believe).