Fresh install is the best way to clear up driver conflicts when upgrading. There'll be so many different registry entries and hidden folders etc it could always lead to problems further down the line.
Whilst it's all up and running now, I would go to your motherboard vendors website and download all the latest drivers, chipset, sound etc. Put them in a folder on one of your drives. Then when you've installed windows, plug in the other drives and install the drivers manually.
Same with CCC etc, get the most recent versions and keep them on the spare drive ready for install.
Steam and Origin games can be kept. Not at my PC, but I think you need to just copy the 'common' folder. If it's default install, the path should be Program files\Steam\Steam Apps\common. Origin has something similar, but can't remember exactly. Once steam is reinstalled you can either copy the folder back over to C drive, or just map it in steam itself. You'll need to 'install' each game, but it will discover the existing files and just download a minimum of files. Back up you saved games as well obviously, usually in My Docs, but not the same for every game.