I don't know about agile and nimble(is that possible with 20+lbs on the bike?), but lower rolling resistance, quick(relative, of course), and reasonable performance, for sure. Those are qualities I want in any situation in which I'm rolling along on a wheel. Agile and nimble would be nice too if it were possible while loaded. I've hit 40mph on my bike while loaded on tour, and had loads of fun blasting down many very windy descents. I'd rather do that on grippy tires with good feedback that are fun to ride than dead feeling tires with harder rubber. I'll gladly change a flat once in a while for the fun and confidence of a nice riding tire. ...Not to mention that weight and rolling resistance thing. It seems like that could be a factor in a 1200mi ride.