There's a thread (well, a few, actually) up on the Bullseye-L forum, QC. Fortunately for us, all of the powders we'd use commonly, with the exception of perhaps Hodgdon Clays, are very fine-grained.

The other thing is how sensitive the velocity is to .1-grain variations. A powder that gains 100 fps over a 1-grain increase is more sensitive than a powder that gains 50 fps. To the extent that a 50-fps swing is even relevant to short-line or even long-line accuracy.

Personally, I'm more concerned with easy-metering powders because, statistically, it means I can get closer to the will-not-cycle point at the low end. And, of course, a powder with a lower standard deviation in charge weights is (again, statistically, anyway) less likely to produce a squib due to bridging.