I don't know much about other exhaust's but I personally really like my WS2. I don't think it's all that deep (so you might not like it) but what I like about it is that it's a good middle between annoying loud and stock quiet, I think it's just right. I have a youtube of my exhaust
YouTube - Apexi WS2 cat back on Prelude the video quality is kinda crappy and I was still breaking it in but I guess it'll give you an idea. The only other thing why you might not want the WS2 is cause its not full stainless steel, only the muffler is stainless steel and if you get snow and salt it could rust. As for more upgrades for hp I'm really not an expert by any means I'm sure other people on this site will point you in the right direction; What about upgrading your ECU? That would help. Good luck