The problem with committing full time to zone read or Matt Schaub is of course the same as the wishbone. You fall behind and you are dead. Griffin can throw it. Tebow can't. But I always felt having McGahee was something that hurt them both last year and this year before he got hurt. Too slow to be a feature back, and doesn't break tackles like a power back
I was half joking about Tebow. I can see what you are getting at though. Everything is fine and dandy running the option until you fall behind. Then you have to throw yourself back into the game. So basically the offense either has to get out ahead, or the defense has to be able to keep you within striking distance. Basically what happened in Denver last year.
It's interesting that you mention McGahee like that, because others on the official Broncos forum shared the same thoughts on him. In fact some wanted Eddie Royal to be shifted over as Tebow's RB, simply because he would be faster and a more dynamic option than McGahee. Similar to what he had with Harvin at UF.