I never really calculate it cause it varies a lot,
depends on notes you play, fingering, does it involves string skipping etc,
I never tried to play 8th triplets on single string and count it,
probably somewhere between 160-180 bpm, just guessing, no idea really!

And best exercise would be to practice the very same thing, 8th triplets, over and over.
With triples the easiest way is to play 3nps shapes for easier coordination
but you can challenge your self by playing 2nps or 4nps while keeping triplet timing.
It's not only the challenge but it'll also sound more interesting music wise.
It's not about speed after all, it's about music.
Let speed be the tool only for creating cool music, do not let it take control.