OP needs to state what kind of money is planned to offer up to this car.
I paid $3k for my blue Golf. It has an 02m (newer clutch), Malone Stage 2 tune, DLC520s, newer suspension and excellently maintained (absolutely nothing needed when I bought it, though I've put in heated seats and a Panzer plate). Might have been a once in a life time purchase, which is why I jumped on it. All said, it's not my DD: my first Golf is, and it is all tailored to me, so, while only a 5spd, is just totally awesome (the fact that my blue Golf is awesome should tell you how awesome MY Golf is!). Anyway, you really have to be at least 65mph on flat ground to run a 6spd. If you can run 70+, and lots of it, then there might not be a better combination out there. Nothing like cracking it up to 80mph in 5th and then shifting into 6th (and having that torque right there to just keep accelerating).
After my experience with my first parts car (2000 Jetta for its seats) I don't think I'd be in a hurry to fetch another one. Yanking a transmission out of one car to put in another one as you're rolling around car bodies (wouldn't think about this w/o a garage!) isn't going to be a snap: and, one has to have the space for a parts car- I have lots of room, so that wasn't an issue for me (though the parts car was on my trailer all the time- lots of parts gleaned thus situated; was going to trailer it away but instead had someone else come get it. And scrounging up parts could also be a pain, time. I'd consider just buying a complete package from Dutch Auto (look in Classified vendor section): trans in my blue Golf came from RyanP (also in Classified vendor section). I priced these out not too long ago (considering options for the daughter's 01m wagon); roughly $900 for a spd package and about $1,900 for a 6spd package- check current prices though.