I believe it might be down to a difference in the way GV100 is designed at a fundamental level. To quote this anandtech article:
"Meanwhile NVIDIA has also made an interesting change to the Volta architecture with respect to how the integer ALUs are organized. Though not typically a subject of conversation in NVIDIA architecture design, the integer ALUs have traditionally been paired with the FP32 ALUs to make up a single CUDA core. So a black of CUDA cores could either execute integer or floating point operations, but not both at the same time.
Volta in turn separates these ALUs. The integer units have now graduated their own set of dedicates cores within the GPU design, meaning that they can be used alongside the FP32 cores much more freely. The specifics of this arrangement get a bit hairy in light of the fact that Volta isn’t superscalar – so you technically can’t issue INT and FP32 instructions at the same time regardless – but given the fact that most GPU operations take multiple clocks to execute, this allows for much more flexibility than before. NVIDIA notes that it’s especially useful for address generation and in FMA performance, the latter of which we’re taking a look at a bit later."
So this seems to make it perform better with integer-type (Primegrid/Collatz?) compute applications. Anyway that's just my speculation.
Yeah pretty much thanks to the price tag, I'm gunna keep it crunching more earnings-focused projects for now. Although I prefer crunching Primegrid over Collatz personally since I like Primegrid's objective more. I'll write a followup article with some more benchmarks, I'll be sure to include Amicable and Einstein.