Russell Day Long seat with backrest and 3" of foam added.
I am 6'4" with 35" inseam so I had them add 3 inches to my seat. I can barely flatfoot it now and my knee pain is gone. When I first test road the GTL I knew that I needed to have the seat raised before I could be comfortable. I also had a RDL seat on my LT so I was familiar with their work. If your knees are cramped on the GT/L, I highly suggest a custom seat with a 2 - 3 inches of foam added.
The GT seat is higher than that of the GTL. I could not sit on the GTL. Tried it out on the shop floor, started to hurt right away.