Like I said before the Roll to Dodge system would be good with a concept like this, if we were to do it here is how it would work with a six sided die. 

[1]-Epic Fail. The action was not performed, and backfired horribly.
[2]-Fail. Nothing happened.
[3]-Partial Success. The exact degree of success is established by the GM.
[4]-Success. The action was carried out adequately.
[5]-Epic Success. The action succeeded in the most positive way possible.
[6]-Overshot. Though the result was achieved, the action backfires horribly due to disproportionately large effort 

What do ya think?