It only took about 8 months, but I finally won all 468 Challenge games. Last one was #327, and it took me weeks to find the right combination to beat it.
I don't remember how long it originally took on 64, so I played it again this morning. Got it on the 2nd try with 23 moves, but that was with a surrender.
OK, I played 64 again, and got surrender in 21 with the game won in 27. I've got severe Slay burnout, from playing it so much, so that's likely to be my best for quite some time.