How to Create a System Image in Windows 7 - How-To Geek
That's how to create a back up image.
Win8 has no performance boost from Win7 in terms of applications. There are some tweaks that make some apps maybe load faster, but actual performance is the same. Boot times are faster, that's about it.
I'm personally not upgrading, even though it's free for me. I have used it on systems on both ends of the spectrum, 3 year old reference board (not even a laptop. just a engineering PCB + GPU etc) to $10K workstations. I don't like it and probably never will. I dislike it so much that, my coworker does my share of Win8 stuff while I do his Win7. Hope that gives you some info from an engineer's view of Win8.