Pretty much what we did Rob
Painted several boats with differant AF, noted which had what and compared at 3 month haul out intervals
Not that much differance, not always dearest that works best
But we now go by word of mouth amongst 400 cruising boats that we take out each winter, off course most are yachts and use self erroding.
the faster boats use harder
I used seajet this year, so theres a hint.
and the darker the paint the better it works
mines black
Charlie