there is no equivalent because mhz is amount of times a cycle can be done on a cpu in a second and mbs is a measure of stored bits and a mhz doesn't imply that you are going to do something new with new files/info, just that you can do those cycles on that machine
in older machines this was kinda proportional but in current machines with multiple cores and doing threads knowing that a cpu most times has sections unused(the reason to use threads in first place) makes hard to say that x amount mhz can do y proportional amount of mbs
on older computers wasn't considered front bus, speed of memory and the size/type of the file to be processed, type of file matters now, not the same to handle 50 mbs of audio to 50 mbs of hd video or 50 mbs of a excell file
what you can do is run test apps like sandra or other sets of benchmarks that will let you how your machine performs when doing a specific task confronted to other machines with similar specs and other bigger ones
when reading some benchamrks in tomshardware you can see that number of cores and specific implementations over a specific technology is what matters now, the mhz race was canceled when multicores won the race
