Looking at the DL data I posted (sourced by someone else) in the 'Major' section it looks like you need 2100 hrs to reach the avg TT of their mil newhire. For the combined civ/mil category you need about 3900 hrs.

So the question is how long will it take to get another 2100 hrs in the C-17? 3900 hrs 121/C-17 in four years is achieveable if you're willing to hustle.

It you decide to fly for a commuter pick the closest one. Is there that's within driving distance? That's choice #1 to #10.