This summer, I helped a friend take down three half-dead birch trees in his yard. He had a cordless reciprocating saw and I had a 21" swede saw with a sharp Sandvik blade. I easily outcut him 3-to-1; he finally gave up and worked the tagline to guide the falling chunks. Even at the top of a tall ladder, I could hug the trunk with one arm and lop off big branches with the other.

Being a cheapskate, I have tried some of the discount blades and have generally been disappointed. It's not about sharpness, it's about the inadequate "set" of the teeth, meaning that the blade binds all the time -- it will drive you nuts. I put one of these in a vise and crudely increased the set with large pliers (note: wear serious eye and face protection). It worked somewhat better, but it's more efficient to buy good stuff right off the bat.

Note that you can resharpen a Sandvik blade with a triangular file. Not as good as new, but they still cut surprisingly well. The added service life makes it easier to cough up the dough for a good blade.