I had a Mach 10 and, later, a Mach 20. I used both in my original IBM PC. I still have the Mach 10 in it's original box packed away with the PC and other vintage gear.
The Mach 10 had a 9.54MHz 8086 that could be toggled to 4.77MHz for programs that wouldn't run correctly at the higher speed. It also had a socket for a 10MHz 8087, an InPort for a Microsoft InPort mouse, and, IIRC, a very small amount of cache ram (1K?).
One interesting thing was that with the Mach 10 installed, the hard drive (MiniScribe 3650 with RLL controller) would run at a 3:1 interleave instead of 4:1. That was probably as big a performance improvement as the faster CPU. (It wouldn't do this with a couple other drives I tested at the time--must have been some special serendipity with the 3650 and/or the controller card.)
The Mach 20 was introduced when Microsoft was still working on OS/2 with IBM, and was positioned as just the thing to run OS/2. I got a copy of the OS/2 version of Excel free with the Mach 20. When Microsoft dropped OS/2 development, I was so irritated that I wrote to Microsoft and demanded to return the Mach 20 for a full refund. Even though I had bought the Mach 20 from a third party vendor, after some wrangling, I got the refund, and a free copy of the Windows version of Excel as a bonus.
I later upgraded the PC with the Orchid Tiny Turbo 286 and then the Intel Inboard 386/PC, and still have them packed away as well.