upgrade time depends a lot on luck, location, and willingness to move. a lot of the southern cal boys upgrade from pa31 to be99 in only three months or so. it's a bit harder to do that in phx or dfw. ofcourse, if you're qualified enough you could be hired directly into turbine equipment.
the upgrade in pay depends on what equipment you're moving into, and what year you are in with the company. 1st year pa31 pilots make about 23k while first year be99 pilots make about 29k. there's a link to an amf payscale listed a few pages back, or you could just go to airlinecentral.net (somebody correct that if it's wrong).
lastly, about the 55k, it just depends on what you're hired into, what you upgrade into, and how long it takes you to get there. i'm just a couple of months short of my three year hire date, and made about 47k this year. it's doable, especially if you're willing to work a bit extra. i know the west texas e120 crews were making serious cash on extra runs, but they did work for it. anyway, hope that helps some.