i'm 6'2" now having shrunk an inch over the past 10 years (how does that happen anyhow?) and i usually have all of my seats within a tiny degree of fully-rearward, but in the S5 I have a surprising distance left to go when i can comfortably operate the pedals.. I notice my knee has a bit more bend to it than normal, which would indicate the throw is longer than i'm used to in a modern car, but it wasn't uncomfortable for me..
before we got the Q7 we actually looked at minivans (god help me) and in the toyota sienna with the seat all the way back, i couldn't put my foot on the brake from the gas without catching it *behind* the brake on the way over - same problem with the town & country too.. strange..
regarding the numb butt, i remember my B5 S4 had a 2 hour warning that would blink when you'd been driving for that long (i assume audis still have that, haven't driven the Q7 long enough yet) to remind you to get up and move around - i think that's sound advice even if you can go 6 hours without aching.. also, you might want to try playing with the height of the front of the seat - if it's too high and affecting circulation to your lower legs it could affect your upper legs/butt as well..