If you already have Ultegra LR's why not use them? They accommodate fenders and larger (than normal for a road bike—I use 28's) tires. They work very well on a loaded bike. As long as you're on paved roads of any sort, there's no need at all for exceptionally fat tires—but that's just me. I feel as though treaded tires pick up glass bits and hold them and increase rolling resistance. I could be wrong, but that's how I feel about 'em. Canti's are fine but I can't see going to any extra expense or compromising your frame choice just to have them. Besides, those Ultegra's are some good look'in (and not cheap) brakes and will do very, very well.