My metabolism is really good and that high of 345 came from tons of stress entering college and a lot of other shit, but I've been blessed because at 6'6" I look like I weigh 250.
When you go to the carnival or fair and there's that booth with the dude that will guess your age, height, or weight I could always fool him by choosing weight.
Genetics are crazy, though. My buddy from high school had never worked out a day in his life, but was a solid 235lbs. at 6' with under 10% body fat, and he was a phenom at any sport he played.