As much as it would be a pain, I've always found a clean install of an OS is better than an upgrade. The only caveat is if the computer hasn't been used for much prior to upgrading. With a well used OS install, it's my advice to do a clean install. You could literally spend days or longer working through oddities caused by the upgrade.
As for re-installing your games on STEAM, the easiest method for this is to copy the entire STEAM folder. After you've done you clean install, install STEAM and log in. Then close STEAM out fully. Then overwrite the freshly installed STEAM folder with your back up. I've done this many times works like a charm. Then launch each game. Any dependencies like .NET. DX, and V C++ that each game needs is downloaded and installed the first time you launch them. Occasionally you'll have a hiccup and all you usually need to do is verify the game cache. In one or two instances I had to re-install one game that wouldn't play nice.
Besides there nothing like that freshly install OS smell.