Thanks much for the responses! Definitely makes sense now. I guess in light of the advantages I'm surprised more tire sets don't do the Dart-Smoke type-combo, although I suppose a good all-around tire will do the job just fine front and back for the majority of typical riders (especially neophytes like me). I have IRC Mythos XC tires now, and am looking forward to trying a different set for comparison and contrast if nothing else. Maybe I'll try the wider up front, narrower in back combination as well.

Thanks again for taking the time to respond.