For croom, and a guy your size, I'd definitely recommend a 450 4-stroke. A friend of mine is a little guy and his 125 is way underpowered at croom. Croom is all soft sand and hills. 2 things you need horsepower for!

Also, the 4 stroke is nice because its pretty low maintenance for regular stuff (you don't foul plugs easily with a 4 stroke). BUT when you do have to work on them, they are alot more complicated and more expensive.