Congratz on finding a gf, I hope you'll have a long & good relationship.
I agree with a lot of these guys, don't sacrifice who you are.
But if you have trouble with women, hide the porn. Real ass is better then tv ass.
I can only partly agree with this.
Hiding something essentially means you're being dishonest about it. I do agree with the part which states that you shouldn't change yourself.
Reading your initial post I get the feeling you don't know her very well yet and you could use that to your advantage.
Everyone 'sins' (I put that between ' ', because they're only sins if you believe them to be so, but that's an entirely different discussion...) & everyone probably includes your gf. Ask her what kind of sins she has committed in the past and still commits these days. Sins she won't/can't give up even though she knows they're 'wrong'.
After she confesses to you she'll probably ask you a similar/the same question (she'll probably understand that you're trying to direct the discussion toward a certain direction). Now I suggest you're honest but tactful. Don't admit you've got X gb of porn on your pc, but make up a nice sentence involving the sin lust (I'll leave that one up to you).
If she's disgusted with it, then she's probably not the right person for you...
On a side note, a lot of Christians (reformed, Catholic, probably Anglicans as well) have a secret stash of porn, so she might not be as disgusted with it as you think right now...