One question I would ask is this: If you took the new job and it did not work out for you, would the door be open at your current employer for you to go back?

It is very common these days for people to leave a company and then return later on for different reasons, and do very well for themselves on their return.

You could take the new job, but make sure you leave your current employer on very good terms, by working hard until you leave, ensuring a smooth and efficient handover of work, and keep in touch with your colleagues etc.

If opportunities are limited at your current employer, I would say maybe it's time to move on. Your career is important, and the danger is that if you stay, to use that awful phrase, "in your comfort zone" for too long, and later on you find you want to move on and get ahead, you might have more difficulty finding a role with a new employer and regret not taking this opportunity. I've seen many people at work say they're happy in their current position, and do not want to progress up the scales, but then later on, for personal and professional reasons, get very impatient and want to move on up.