Namaste RJE,
The X16 is INCOMPATIBLE with thousands and thousands of C64 program
The c65/m*g* 6* is 100% compatible with 3 computers ie. CO*MODOR* 64, CO*MO*ORE 65 (prototype,unreleased) AND EXCLUSIVE MEGA 65 MODE
Note that the Mega 65 has 40 Mhz Clock speed,inbuilt 3 1/2 inch floppy,SD card 100 freeze slot to freeze your programs, on the fly clock speed change and all previous c64 hardware and many more for the same price.