Don't discount flying some on-demand 135 charter, either. You'll learn more in a shorter time flying piston twins in and out of diverse, remote airports than you will flying a regional jet in and out of the same regional/hub airports for a month at a time off of the same canned flight plans. Find a good large charter company and you'll be able to progressively upgrade through turboprops and into jets.

I know a lot more people that went straight from a 135 job directly into the majors, than left a 135 job for a regional job. The turnover is high enough that positions can be found and you'll probably make about the same, if not more at a 135 than at a regional, at least for the first several years.