For what its worth, I have recently played a bit of 25NL regular tables on ACR Poker, and I think, they are not all that tough. Certainly something, which I feel, a player solidly winning at 10NL should be able to beat. So I think, the main issue for OP is the BLITZ format and not the transition from 10NL to 25NL. Even having been away from cash games for 5+ years, I would not bother to begin any lower than 25NL, if I was to decide to go that way on ACR Poker.