I am 5'10".5 and rode a large and it was comfortable for riding aggressively. At 6'4" you should be on the XL Heckler. You will find the large to be cramped regardless of what stem you use. I used a 55 or 65mm stem on my large.hac0555 said:i am looking to get a heckler for some very aggresive xc and some fr i am 6foot 4 and about 160 i am woried if i get the xl it will be too large for jumps and i found a large allready any help i can get would be great