If you spend the time time messing around with the BOILING_POINT and SPEC_HEAT tokens you can get it to where the blood will remain for a short period of time before evaporating. I messed with this in arena mode with my cat mod and eventually managed to make it work, but it's really titchy in terms of the values you want to use and probably not worth it.
That's what I was going for, but I never saw any effect from changing Spec_Heat. If you can remember how you made that work, I would be interested.
So it is as I was starting to fear already. No change for me either, though the maps are still bloody as I have no cleanup tools to use. -- This FPS loss is due to some bad programming elsewhere, though imo, related to contaminants. Or the cleanup didn't really effect the things the game keeps track of. Anyway, I am more and more of the mind that this is just a serious case of bad programming and design.
Maybe we have a ton of invisible vermins that eat the FPS? I know my fortress is littered with flies and rats picking at the corpses now...
I suspect the coatings. Each contaminant applied to each item and body part creates its own object. Washing a dwarf converts blood coatings to water coatings, which presumably eventually evaporate. But until that evaporation your FPS would stay unchanged.
My best idea right now is lots of wells. Dwarves will use them to wash off, and I think they come away with no coatings.