gotcha.  that's kind of what i was thinking in terms of grayscale vs. color, and i'd noticed the asNumber() trick, but i've been lazily relying on Matmatic to optimize so far and not considering ways i could optimize. 

so there's no function that would spit out the min or max of a result?  i was thinking that one would be obvious, but i just wasn't bright enough to figure out how to use math nodes to discover it.  i'm just thinking, it's not the function in the abstract, but an actual result set.   i feel like there must be a way to get the min and max from a result set.  but then, there's lots of things i feel should be possible and aren't.

thanks so much for your help.  you've explained a lot.