one of the more popular things right now is a hybrid tranny combining gears from ls and gsr. i would think you would want a gsr trans with ls 5th or whatever housing you want. how often are you going to be driving in 5th vs racing in 5th? pretty sure you wont hit 5th on the 1/4 and i pray that you arent going so fast through corners that you need a gsr 5th.