Your times for that Titan V on Seti look way off. You aren't showing what applications you are running for that work unit. If I had to guess based on time to complete, I'd say you are running a cuda 3.2 You should repeat the test and at a minimum run the cuda 5.0 application or better yet run the OpenCl SoG. Ithanul is correct that you should be devoting 1 core to each GPU, especially for the OpenCl.
There was another Titan V on Seti about a week after it was released. His times to complete were 1 minute 23 seconds I believe. Comparable to the Special Cuda 9.2 application from Petri.