I wouldn't say that LT's even benefit SOUND; my buddy hates his because when we had the exact same cat-back with O/R H-pipes and same motor setups, but his was only 1/2 as loud/deep as mine (and I just had OEM shorties). It seems that LT's will tend to change the exhaust NOTE slightly, but they also tend to reduce the VOLUME so much that the change is hardly even audible. That, and LT's are a pain to install; shorties are relatively easy to install (except for equal-length designs or GT-40P's), but they cost a lot for gaining practically nothing. You'd get, what, MAYBE 3-5 horses at best? Hardly seems worth $200+ and a lot of install time and headaches ... especially if you wind up snapping an exhaust bolt or two off in the process.
Invest in a set of pullies, and K&N panel filter, and a nice off-road H- or X-pipe and call it done - you can have all for the price of one average set of LT's or good shorties.