I'd be very surprised if the MTH steamers are geared that low, I believe they're more like 18:1 I've recently worked on several Williams steamers where I actually was computing the gear ratio, a brass K-4 was 28:1, and the Williams brass Niagara was 44:1.
Actually Ted, I have stated several times that 24 stripes is "standard" for MTH PS/2 or PS/3 locomotives. As far as adjusting speed, dropping a stripe or adding a stripe from a 24 stripe flywheel will change the speed around 4%.