Old thread, I know but I have a short story about slotted pistons.
After thrashing my Atlas on a long weekend ride of several hundred mountanous miles, I was about 100 miles from home when the bike started running on one cylinder and vibrating differently. Parked the bike at a farm, rode pillion home with one of the other guys and went back later with a pickup to fetch the bike.
On tear down, one piston remained at the top of the bore while the engine was turned over. Pulled it all apart to find that a slotted piston had failed, leaving the skirt and pin intact. The bores remained unscratched so I honed them and fitted new drilled pistons sourced from Austrailia. I think they came through Rabers. The failed pistons were 0.030 oversize so these slotted pistons had gotten into the spares supply chain. The Austrailian pistons had very tight pins and had to be bored on the pin fitter. I don't recall what the cylinder clearance was. Once installed there is a slight piston slap when cold but goes away in a few minutes. Thirty years on and much more thrashing it still runs fine.