8 minutes is too long, even for a hdd. With SSDs expect start ups 8-30 seconds, depending on just how much crap you are loading up at windows startup. With HDD's you should be 2-5 minutes at worst.
Swapping OS is a start, but since there's no change, it's elsewhere. I'd suggest you install the last bios update for your mobo, and update audio/Lan mobo drivers. Since you have win10 registered, I'd use CCleaner and run it several times as well as using tools-registry cleaner. You can set it to remove all the win.old files as well, which is all the old win8 files that do nothing but take up space. I'd also do a good search of your startup stuff and either disable things that really don't need immediate loading, like Adobe etc, or set for timed loading after windows is fully booted.
I'd also run malwarebytes or hitman-pro (add root kits) for anything that could be causing issues.
Samsung 840pro, i7-3770K @4.6GHz. Cold boot-internet 23 seconds. That's with hibernation/fastboot removed.