Ultrabook dilemma, what so I need?

So basically, for weeks now I have been looking at reviews and specs of all of the major Ultrabooks, and am confused as to what I need stats wise.
Im really attracted to the m series, with it's fanless design, but I'm not sure if I will be sacrificing performance massively.
I will be using it at University, so I need to to have a long battery life and to be able to handle word applications and web browsing without any hassle.
It's important to me that when purchasing a laptop that the performance doesn't feel second class when performing these tasks, so I was wondering what you guys though the best options are for me.
I want 8gbs of ram
Snappy performance for word and browsing
Slim form factor
Backlit keyboard could be a deal breaker
And great battery life
Price is MAXIMUM £700 ($900) but preferably less,
Hope you guys can help!

PS not bothered by fancy screens, if anything I prefer the battery life of non touch 1080 models