im in a similar postition mate.
ive had 14 fights, lost the first and won the rest, 11 of the 13 wins though KO
i weight 200lb, and im 17 years old, and im 5ft 10 but i got a problem.
i can punch AS hard as the other heavies, but im not susally stronger than them. i reply on my hand speed to win the fights for me.
im thinking of losing weight and trying to get down to middle weight at the moment, where i will be able to punch much harder than the average, and my hand speed will be very fast aswell, going for the easy wins.
dont fight at super heavy at 5ft 11 unless you hit like a train.
i spar with a super heavy, but hes 6ft 7, and 270lb. i dont know whether you would stand a chance of beating him if your only 5ft 11 ish like me

i advise you to fight at a lower weight, but no so low that you lose your natural abilities (mine is speed and heavyish hands)

hope this helps. PM me if you want more help, that goes for anyone

alex