After tinkering and ripping and reknitting, I'm finally happy with all the details in the mitt; the slipped-stitch ridges in the garter cuff continuing over the stripes make me especially happy (as does the gusset. I like gussets, and particularly the way the slipped stitches curve around this one).
I'm writing up the pattern now, in two sizes. This is the smaller size: 6 1/2" around (my wrist is 6 1/2" and my hand is 7 1/2" inches - these are snug on me and I think they could fit a hand a bit larger and definitely smaller, too). The larger size will be 8" around - I'm making them for Jacob, whose wrists are 8" and hands are 10". I'll be reversing the colors for his mitts.
I hope to have the pattern available for a group of interested testers later on today (I think I'm all set for test-knitters now, thank you!)!