I'm 6'3", most of it in my legs. There's not much leg room. Different people have different tolerances for comfort. It's worth comparing to my old Mk II Roadster, in which I modified the transmission tunnel aluminum to make sure the high-back seats were square, faced forward, and the driver's seat was very nearly centered on the steering wheel. That made it comfortable enough on the street. A lot of people mounted their seats slightly crooked to clear the transmission tunnel and were perfectly happy, but I couldn't get used to that - different strokes, etc. etc. The track really highlights any ergonomic issues. Having my feet off to the side in the Roadster (the footboxes are offset to clear the bellhousing) felt awkward on the track. I also wished I could have been more reclined on the track and cinching down on the harness put too much downward pressure on my shoulders.
The leg room in the 818 is about the same - you just don't have the bellhousing pushing your feet to the side.
I completely re-structured the floor of the frame in my 818R to allow my seat another inch lower and more reclined. I then re-structured the pedal box area to push the pedals about 4 inches forward. It's still not roomy, but definitely a lot better than my Roadster was and how the 818 was from the factory. Also, the steering wheel in the 818 comes up at a slight angle, so I re-welded the steering column frame tab and put together an aftermarket u-joint assembly to make it straight and perfectly centered on the seat. The bolsters in most racing seats will push your knees up into the steering wheel if you are tall. I moved the steering wheel slightly closer to me to help that, and getting a slightly smaller-diameter aftermarket wheel is on the punch list, which should make it perfect. The new position will absolutely require a quick-release steering wheel hub, though.
I'm building an R, not registering for the street. Here's a link to my build thread where you can see what I did. I probably wouldn't go to all that trouble if it was just going to be a road car....... but if I wanted just a road car, I would have kept my Roadster - nothing sounded better...
http://thefactoryfiveforum.com/showt...R-Build-Thread