i don't think the fact that whether if it's new or not will affect how loud it is, if it's the exact same model BOV you're comparing....unless your 2nd-hand SSQV is stuffed....faulty spring etc etc....
also depends how much boost you run, and if you have a FMIC(which i have btw)...dunno how much difference will it make in regards to the mounting position though, mine's mounted where the stock one use to be....
if you want just the loudest ones around, get the BLITZ DD...it can get really loud....as well as the higher end GFB ones....