How much battery life do you get on bootcamp windows 7/8?

I have a macbook air with i7 and 8gb i got yesterday.

I got it mainly for school as a gift. One problem, i am windows guy.

I actually like it allot its pretty cool. This thing would be perfect for touchscreen.

Anyways, when im not at school(architecture sf academy art) its windows 7 i have on bootcamp. Whats your average battery life on windows 7/8? Would it be better to have windows 8 or 7? I currently have 7.

Also, are there any overlay usb touchscreens for this?