$25 NL on every site I've ever played it beatable. You probably already have the skills to beat $25 NL if you're beating $10 NL. In my opinion it's more a matter of being pyschologically prepared to move up a limit and making the proper play adjustments. The play may be a little tighter and the players slightly better, but they're still bad enough that you should be able to crush them once you get a feel for it.

If you've been playing $10NL for that long and made that much money then you really need to move up. It's time to step-up your game and step-up your earnings. It may take you a little time to get use to the larger amount of money at stake and the tighter play, but soon you'll realize that you belong there.

I encourage you to keep seeking advice and post hand histories as you make the transition.