What you might do is take your seats out and look at the factory rails. I am 6'8" and on a lot of vehicles that I have owned the factory rails will have differnt spots marked for holes to attach the seat. Drill out the holes and remote the seat in the new holes and you will usually gain a couple of inches of movement. If you really want to get a lot of leg room then it will probably be easiest to go with aftermarket seats and then you can mount the rails how you want them. I did this in my last car and it was awesome, there was not way anyone could sit behind me, but I had to fully extend my arm to hit fifth gear.