I'm 6'5 and a tanker. I know a couple of others who hit 6'4. (There are ways around the 6'2 limit if you know the system :-) )
The driver's hole might be a little uncomfortable, but not very. I'm all leg, so the gunner's seat is definitely the least comfortable for me, although it's really a relative statement, and I quite happily ran a few missions sitting there. Indeed, in order to manually operate the elevation handle, I need to move one leg behind me as if I were kneeling on my left leg. You may have slower loading times as a loader, if you're too tall, there's not enough room to 'flip' the round, but it's not a major issue.
I don't know if Arty or Engineers are any better or worse than tanking. I just know I love tanking, and so does pretty much every other tanker I know. We're sortof a culture to ourselves, I guess. (We're also theiving bastards, so watch your gear)
Good news about being a tanker.. Hmm.. Your weapon carries you instead of you carrying a weapon. Your personal load is restricted by how much room is on the tank, as opposed to how much you can carry on your back. In really cold weather, the exhaust makes a wonderful heater. A tank crew is about as intimate/close a gathering of soldiers as exists, since you're all in the same box, on the same intercom system with nothing to do but talk to each other for quite a lot of time. Lots of ways to play with the new guy. You get to call infantry types 'crunchies'
Bad news: Track maintenance. It sucks, it's dirty, and as the junior man, expect it not to be pleasant. Everything on a tank is heavy. Be resigned to training on tanks, then going to Iraq in a HMMWV. You might get lucky, probably won't. Infantry types will call you a DAT/CDAT.
NTM