I've read that on average battery life, on a new laptop with Windows 7 and 8, Windows 8 will add about 30-45 minutes to.
I have read this too, but until I can see it for myself and quantify the difference, I will remain skeptical.
But in real world comparison, 8 just feels faster and snappier.
I think a lot of claims of speed are based on the gut feeling of "it just feels snappier". I am often scoffed at for my claims of not noticing speed improvements outside of bootups, but when I ask others if they did time test with stopwatches or other devices (like i have) they always say no. Then you find they compare an older load of Windows 7 with tons of cruft, to a new machine with new hardware and a fresh load and say, "Wow, look at how much faster it is". Really, it's faster!...this surprises them? It's faster hardware and a fresh load.
I on the other hand, take 2 identical machines from work inventory, fresh load Windows 7 on one and Windows 8 on the other and test and I see very little difference. No doubt bootups and shutdowns are faster. But for most other things, I challenge others to prove to me it's faster....i've got my conclusive proof saying time difference is negligible.