Is it worth changing sixth forms?

I'm a year 11 and I'm in the process of deciding where to go for my A-Levels.

The grammar school I currently go to has a sixth form which I can move on to, nice and easy. It received a "good with outstanding features" rating from OfStED and from what I hear from students there, it isn't too bad.

However I also have another option. There is another Sixth Form in the country which is pretty damn good. It received an OfSTED rating of "Outstanding", is supposed to be one of the top 10 in the country, and is full of the brightest students around due to it's hard entrance requirements. It also produces a fair number Oxbridge students as well. I've applied, been given an interview and I'm waiting on a response.

Now if I do get offered a place, what do I do? I really enjoy English and I'd love to read it at Oxford; would moving to a superior sixth form dramatically increase my chances of doing this? Is moving to a different school at this stage a bad move?

I think most of me wants to stay at my current school, yet I don't know whether there is enough to justify this decision. In the long run, will I regret staying? Will it hamper me?