What size dirt bike do I need?

I'm 6'3", about 175lbs, going on 20 years old, and I've had several motorcycles. I currently have a 2005 Honda Shadow 750 (for the road). Before that, I had a 2001 YZ250, and LOVED it. Well, here I am wanting to get another dirt bike for offroad. The thing is, although I absolutely loved my YZ250, it was a bit too much power for me to be able to open up on my farm, and with a 2 stroke, it's either wide open, or nothing. So I'm thinking about getting a 4 stroke this time, but I'm not quite sure what size to get. What do you guys recommend?

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