Seniority...Seniority.... If a bid comes out to fill vacant seats, you bid and if senior enough you can hold it. You could go from a 727 FE to a MD11 captain if you could hold it, though I would not do this myself. The progress from the FE seat is usually to the right seat of the 727 for those more interested in quality of life, and to any of the wide body FO seats for those more interested in money or modern equipment. It all comes down to a couple things:
1) Do you live in domicile or commute
2) What quality of life do you want
3) Where do you want to fly
4) Are you money hungry(in no particular order)