I regularly track 2 of the cars mentioned above - mostly stock rx8 and e46 330i that's completely stripped with race seats. I'm also 6'2" so I can relate to the fitment issues, here are my thoughts:
RX-8:
Mine is mostly stock, only mods are springs and sways - full factory interior. I generally let my novice friends drive it for HPDE, and they have ranged in size from a former nfl linebacker, to my 5'8" neighbor. They've all been able to make it work, though I have two seat pads, one with the foam removed, and 1 that isn't modified at all. That said I can't fit in it with a helmet on without completely removing the cushion and sitting on a cut yoga mat(ouch). I do have a sunroof model, and w/o sunroof I bet I'd fit just fine in the stock seat, at least the one with most of the foam removed. The wheel doesn't telescope so leaning back is not an option unless you have really long arms(like the previously mentioned linebacker)...
On the Track, the car is a blast. With decent pads, the stock brakes are incredible. It's pretty light and has a factory LSD. It's really easy to drive fast, yet still pretty capable in the right hands. On a medium tight track, it will hang with and even pass much more powerful cars. I will say that prior to the new springs/sways, it did have some pretty substantial body roll in the corners, but that was a cheap upgrade and it's dead solid now. In 2+ years of tracking it multiple times a month I've only replaced tires/pads/and a couple $15 solenoids. It really seems to like being run hard!
e46 330i
With race seats(not even in their lowest position) and the interior stripped I have several inches of headroom, even with a helmet on. Prior to the race seats(stock) and when it still had the sunroof(since deleted) I fit comfortably even then. The wheel telescopes and moves up and down and it should be easy for just about anyone to find a decent driving position.
On the track, It's my favorite car(that I have). Super well balanced, and though the rated HP#'s are similar, it has more grunt than the rx-8 by a good margin. To be fair though, the engine is a ZHP motor with catless headers, CAI, 3.38 rear diff(currently at the shop getting a 3.46 lsd installed) underdrive pulleys, and an aggressive tune. Still, I do remember it having more power than the rx8 when it was stock and 400 lbs heavier. It goes through consumables a bit faster than the Mazda, but not excessively so, and has been fairly reliable(if you don't count the original engine that had 135k on the clock when I bought it and likely wasn't cared for well based on the condition of the rest of the car) I've also addressed all the common failure points(cooling system, oil pan baffle/pump nut/chassis reinforcement, etc. etc.) so that may contribute to it's reliability. On similar tires, I'm about 3-5 sec a lap faster(on a ~2.27 mile track with 14 turns) in the e46 than I am in the mazda, though at this point it's not really a fair comparison as the e46 is probably 90+% of a true race car while the rx8 has only minor mods. The biggest downside to me is that all non-m e46's came with an open diff, and the M diffs don't fit. There are plenty of ratio options to be had by swapping from the different e46 models, but none are limited slip. If an LSD is important to you, plan on spending 3k(including core) if you do it yourself, more if you have to pay someone to do it. That could be a deal breaker, as that's probably close to the price of the entire car, more than half anyway, whether you went e46 or rx8.
TL/DR: The e46 330 and the rx8 are both awesome track cars with tons of potential. If you are concerned about fitment, you're fine in an e46, but make sure you find an rx8 w/o a sunroof, otherwise be prepared to sit in the seat pan or have race seats installed.
Hope that helps!