If you look at 68000 instruction timings:
http://oldwww.nvg.ntnu.no/amiga/MC680x0_Sections/mc68000timing.HTMLYou'll see that there are plenty of instructions which will complete in the equivalent of half the number of clocks with a 14 MHz 68000. Of course, all memory accesses continue to run at 7 MHz, so on a CPU which needs to load all instructions from memory, the speed is largely limited.
The 68010 goes well with the 14 MHz speedup because it has a special loop mode where a loop which consists of two instructions (three words total) can be run without refetching those instructions, and therefore can run at the full 14 MHz.
