the question was which Windows release ... because a Windows license
Reuse your exiting 7 license if it's valid, or:
8.1 64 OEM ($100)
8.1 Pro 64 OEM ($140) if you need Bitlocker, Hyper-V, or a $10 Media center upgrade (it's a $100 upgrade on non-pro versions).
MS relaxed the OEM restrictions in 8, but I've never had a problem with multiple 7 OEM or 8 OEM keys for reinstalls or full upgrades. You may need to call their automated 800 number to reauth it, but it's simple. Just delay activation until you get your OS and apps configured.
The 8 hate gets overblown. Set 8.1 to boot to desktop and change the Win key to show the Apps (aka full screen start page) screen instead of the Metro tiles and you'll never see Metro unless you want to. Win+X brings up a context menu with every useful settings/config panel. Or install a Start menu alternative for a full 7-like experience. 8/8.1 do have technical improvements over 7, requires less patching, and supports more hardware out of the box.
With the current state of VM software, you can game natively in Windows and do everything else in a Linux VM if you wish. No need to dual-boot. I used to use Linux exclusively but gaming and a m-card tuner are what keep me on Windows. I also used to use Linux to be different, but as I get older I find I don't can't what I use as long it does what I want it to do.