Comment by Michael Huth (enigma[at]mail.lipsia.de): The MOS6510 is a 6502 with an additional 6 Bit bidirectional I/O Port. (The pre-release spec of the 6510 mentions a 8Bit port and since there was never a official release specification of the 6510 all literature copied the version with the 8Bit wide Port. Maybe it was planned, but in the end the 6510 got only an additional 6Bit.)
The 6510 (and the 6502) can run also at 2Mhz.
So does the 8502 version in the C128 Computer and the 6502 in the 1571 Disk Drive. The 6510 that was built in the C64 ran at 1 Mhz, so it was compatible to the VIC2 Videochip.
References: Preliminary Datasheet