Hey thanks man! Those look waaay more optimized than my routines. The main difference being that I was thinking my sprite drawing routine should do the heavy lifting of masking out the buffer and putting the sprites in place, instead of actually using multiple buffers. Seems a waste of cycles and memory otherwise, but maybe I'm not seeing something ;) I'll give it another spin, see if I can't get it sped up a bit with these ideas.
I also wrote a second implementation that doesn't use a buffer in memory, but that has some logic in the background drawing routine to mask out the foreground sprite. So the background just leaves a "hole" for the foreground to render into. Much less slow, but I'm a bit scared to go down that path because it requires a lot more bookkeeping in the background drawing routine, which may get hard to work with as the game gets more complicated...