I know how you feel CarstairsCowboy. Even though I've grown up loving the military and guns, I've only ever fired a .22, a Spanish shotgun and an M9 - each on one occasion only - so my 'first-hand' knowledge of firearms was also quite limited. In short I never held the weapon I wanted - an M4.
I finally got myself an airsoft all metal M4, and all I can say is, no one could have told me what it felt like. You just have to try it. The weight was a little uncomfortable at first but after playing around with it for a week I felt much more comfortable(though I can really see the benefit/leverage of a foregrip).
If you have personal access to a store I'd say go in and feel a few of them if they let you. That's really the only way to know for sure what feels right, but keep in mind anything new is going to feel a little foreign at first.
I agree with the post that steers you in the direction of something like the M60 because in my opinion they were made for guys your size. They ain't light either if you get something metal. Add a foregrip to one and man that should be fun.
Keep us posted as to what you get
Here we are again bro -just you and me. Same kind of moon same kind of jungle. Real number 10 remember? Whole platoon, 32 men chopped into meat... We walk out just you and me, nobody else. Right on top huh? Not a scratch... Not a fuckin' scratch... - Sgt.Mac, Predator