I am not sure what you want to know is stronger. The overall impact on the DV of all regressors (adjusted R square might work, but only if you use the same sample for the two regression equations otherwise its an invalid comparison I believe). Or do you want to know, within a given regression, which has the greatest impact? In that case this might help.
If you know if a specific regressor had greater impact on one DV than another I think you have to use the same sample for both analysis although I could be wrong. I would think if you do use the same sample you could use the approach in the thread above.