Hi all. I'm ready to move into a different bike, and would love some guidance. here's the quick and dirty:
1.) I am 6'5", about 370 lbs. I have lost 80 lbs so far, purely by cycling.
2.) I ride about 12 miles to work a couple of times a week, all on urban roadways.
3.) I also ride once or twice on the weekends, and am hoping to extend those rides to 50 miles or more at a crack (they're currently 20-30 miles)

I have looked at a Giant Escape 1, and am also intrigued by the Specialized Sirrus Sport Disc. I am targeting a price point of $600-$800 USD, but will go higher if the bike will serve me better as both a commuter and a decent set of wheels for long rides.

Here are my specific questions:

a.) Are there any glaring problems with the two models I mentioned?
b.) Are there other models I should add to my list?
c.) Are there any real advantages to disc brakes? (I've never had a bike with discs before)
d.) What other questions should I be asking?

Thanks in advance for any help and insight you can offer.