in my opinion, HKS sounds best with a catted downpipe.
With catless it's more on the raspy side and too aggressive for my taste. if you are looking for a more aggressive than average sound, you will like it.
Per PTF (bm3)
Stage 1 91 octane: up to 22% HP / 25% TQ
Stage 1 93 octane: up to 25% HP / 25% TQ
Stage 1 E30 octane: up to 28% HP / 27% TQ
Stage 2 91 octane: up to 26% HP / 28% TQ
Stage 2 93 octane: up to 28% HP / 28% TQ
Stage 2 E30 gas octane: up to 34% HP / 30% TQ
stage 1 is stock, stage 2...