I am a large man, 6'0" and 290lbs. Will a mid size 4x4 ATV in the 300 to 350 class be large enough for me. I want a smaller easy to manuever quad.

 

No way. Start with a Honda Foreman 450, now with switchable 2wd/4x4, forget the Electronic shifter, or look at a Polaris Sportsman, 500cc.
The 350 class is the Honda Rancher, not bad but pretty basic, and pretty gutless with your gut on it. (sorry, couldn't resist) or a 325 4x4 Polaris Magnum, pretty anemic. A Kodiak is a pretty good mid-level 4x4.
.......Ride em, ride everything you can. Dealer parking lot rides can be very decieving, try to get a real ride on everything you can. Under 500cc I think the Foreman and the Kodiak are the best, forget about anything smaller, you'll just regret it and wind up trading up later anyway.[img]i/expressions/face-icon-small-cool.gif[/img]