Have you considered that if you had gotten an EA job, your impact would have only been the difference between what you can accomplish in that job and what the next best person could have accomplished? As so many people apply to EA jobs, this difference would probably not be very big. 

By getting a job outside of EA and donating, your impact would be almost completely additive as it is unlikely that the next best person that would have gotten the job would have been EA and donated themselves.

Especially if you have high earning potential this effect should be  large.