I don't think there is that much difference between a 25, or 30 or 32 tire. There may be a slight difference in the rim. Wide rims can't go smaller than 28 and thin rims can't go larger than 25. The key is to get either one of the armadillo or one of the marathon tires with kelvar so you don't have to worry about flats.

A 2 hour ride is a long ride. There are 2 different schools of thought. One says you want the lightest bike, i.e. sport road or performance road bike. The other school says, hey this is long, lightness doesn't matter with that much pounding as much as comfort,i.e. cyclocross or touring bike. If it were I and I had a 70 minute or less commute, I'd go performance road bike. With your distance, I would go with cyclocross or touring so I could use the wider tires and use their shock absorbing abilities to help me feel better at the end of the ride.

If you can afford it, a cool commute bike might be the Litespeed Blue Ridge, it's TI so no corrosion, very light and yet designed for longer distances. Only disadvantage is it has regular brakes, but you should be able to custom order one like it with disc brakes.
I don't know about the merlin line, but they also have a great rep.