Pop fps before fps after
51 50 60
80 28 28 (that was the bloodiest fort)
58 73 62
try again with a huge fort (min 300 creatures pets + dwarves) where fps have dropped below 10 (if you butcher 3 cats or war dogs which "wear" some blood, performance will likely go up 1 FPS. in my experiment it was like washing 2-4 dwarves from blood and cleaning that away with dfcleanmap (run in a loop with "dfcleanmap -q") improved FPS by 1)
or wait inside the fortress for some merchants getting killed outside ( at least 100 dead outside), then send 'em all outside gathering refuse (o-r-o)
you will see a HUGE performance drop (mine went from 25 fps down to 10)
my last fort was on 100 FPS with 28 dwarves, after i equipped 1 (!) hunter with a crossbow, and after he killed around 30 animals which were hauled to the butchery, performance dropped to 60.