To answer your question, I am 6'4" and had no problems with the TQ. When laying perfectly straight the quilt came up to the tops of my shoulders. Once I "snuggled" down into and bent my body slightly I was able to pull the TQ up over the top of my head. It was quite toasty like that I must say! If I had to put a height limit on these TQs I would probably go with around 6'6" or 6'7".
If you have major concerns I would just give Marty a call and you could probably get him to make one a tad bit longer.