iPhone 5 and iOS 7

So, I have an iPhone 5 since march and I am very happy with iOS 6. Now my phone downloaded automatically iOS 7 and I have 3 gb less and the battery drains more quickly than before.

I don't hate iOS 7 new colors and layout, so the question is: the battery will lasts more time or at leasts the same time like with iOS 6? And the 3 gb will be occupied forever?

my phone will be slower? Should I upgrade to iOS 7?

Thanks