I'm having the best luck with Dunlop chloroprene bx40's on shimmed tjt/gy6 pulley setup. Some bikes/variators only accept an ax40 like polini variator/stock rear pulley. I usually get 2500-3500 miles per bx belt on a 65mph bike.
The variation in belt thickness is interesting I'll start paying more attention to that. Non of these belts truly match the cheek angles either but hey,it's just mopeds.