Fps mean next to nothing.
And the difference between decals and vector paint is likely infinitesimal so not something that can be benchmarked in a finished product.
You can set up a benchmark, with say 10000 decals. But then you literally wasted your time making a benchmark that will never give you a true cost per decal value.
Same with vertex paint except since that is always active after a material is set up you know the cost almost immidiately based on material instruction counts…