I'm afraid from this thread and previous ones I remember it seems clear your current employer is dangling the possible promotion / payrise as a carrot and aren't necessarily going to follow it through.
Your loyalty to them, while positive sounding to an extent, is clouding your judgement here a bit I feel.
They could have given you a 3/4/5k payrise at some point during the last few months if they were very serious about keeping you. They are underpaying at the moment, you are obviously very good at your job, so it would make good business sense for them to spend a few grand on retaining you.
The fact they haven't done this as a gesture leads me to believe they will try to keep on as low a salary as possible for as long as possible.
They may value you but they don't sound like particularly good business people if they are undervaluing you as an asset and therefore risking losing you.
I wouldn't want to work for a company that showed they undervalue solid, capable workers to the point they are underpaying them to the extent they are you. It would make me think they weren't especially efficient business people as they should be trying to retain great staff at the moment but seem very green in risking you leaving.
And that leads me to question that maybe rather than them being green or inexperienced, they are just confident you won't leave and don't believe you'll jump ship. That wouldn't be attractive to me as an employee either.