Originally Posted by Bullit79

I have 18" resonated. I too was on the fence on 12" vs. 18", but I love the 18's. When cruising at highway speeds, you can still hear the purr of the exhaust and then when you get on the throttle, the purr becomes a roar! (But nothing obnoxious)

Later if you still think 18" is not loud enough, you could just order the x-pipe from FI (with the 3 month wait time) or see if anyone would be willing to trade their 12" for your 18".
Also, the dent/scrape on there doesn't look too bad IMHO. Probably doesn't affect sound or performance. You could probably give the guys at FI a call to get a 2nd opinion. They're more than happy to talk about their product.

EDIT: BTW k-series crew checking in. Still have my NHBP '05 RSX (base) as my semi-daily driver.