From my experience with the 6 speed it should be our only option, at least for those that are boosted anyways. But even in n/a form the 02 gearbox or p12 gearbox makes for great gearing in n/a form. The 03 and especially the 04+ is great for turbo. My gears are almost identical to my 99 p11 gearstack that i had in my b13 trans with the exeption of 4th gear being a bit shorter. however 5th gear is just as long and then basicly add a 6th. I was crusing on the highway at 60mph at 2200 rpm vs almost 3000 before. I love it and I put some pretty hard shifts through it on the street with the twin disk clutch that before I COULD NOT DO on the b13 trans without shattering the teeth off 3rd or 4th. I did some no lift shifts 1st-4th and then still quick shifted to 5th and kept going under 34 psi and not a single problem.
Not to mention the spec V trans shifts like butter. Seriously it doesnt hang up, doesnt grind, takes to no lift shifts very very well. I know the 02-03 spec v boxes had syncro issues but those were resolved in the 04 box.
I think its gonna be our only option out there. For the n/a guys you really dont have to worry about breaking gearboxes even with the 300whp n/a guys.