I would definitely move up to 50 NL with a 1900$ 'roll. The fact you got it by bonuses doesnt matter, its your money whether you win it on the tables or are given it. Your goal once you are at 50 NL should be just to break even for the first week. This is all you can expect, since the players will be tougher. As you get better you will begin to beat it, and eventually you will make more money than you could at 25 NL.

Dont worry about the 5BB/hour winrate, its a good enough winrate to get your 'roll up to 50 NL standards, and in my opinion, thats good enough to move up.

If you dont move up, youll be stuck at 25 NL forever and youll never get to 1000 NL where you can make serious money. The only way I got to 400 NL was by moving up whenever I was bankrolled to.