for what purpose? just as an alternative to your every day board or as a groveler? fartknocker would make a better groveler b/c it has more volume than the sperm whale. SW seems like more of an alternative type board. very low volume (IMO) for the design.
never ridden the fartnocker, but the sperm whale is FAST. i rode it in waist-chest high mush and the thing flew through sections almost feeling too fast at times, so i have no doubt it would be fun in really small stuff too. it's not great if you want to do turns and stuff though, and you can't really bottom turn on it. the fartnocker looks really fun though and i'd really like to try it out