Be careful of what you treat timbers with (assuming you are using green timbers) you don't want to lock water in the wood.
I'll second Emmett's coment on sealing end grain, a small tub of Anchorseal has become a standard part of my timber framing kit.
I'd say go with the White Oak if at all possible unless you've got the budget for reclaimed Chestnut, there are always ways of handling more weight. My wife and I installed our entire sill structure including a 20' 8"x9" Hickory sill (~630lbs.) up onto the foundation by power of lever, roller and hand.
If you don't mind me asking, where in CT are you? We're in Warren which is in western Litchfield Co.
