You forgot to mention your LS is automatic. There are endless possibilities, but then there are variables. I'm sure you have a budget right? What's that budget amount? How much HP do you REALLY want?
Well, the purpose of the LS 5th gear is to save gas during highway cruising. You don't wanna be running 65-70 @ 3K-3.5Krpm's lol. I got an LS with GSR tranny, it picks up nicely, but gas kills me.