There's a couple problems... one your 8th generation Intel CPU won't function correctly under Windows 7 or 8.1 as it'd only have generic support since Microsoft + Intel don't support CPUs newer than Kaby Lake in Windows 7 and 8.1. Which is to say that you'd have to use Windows 10 to get full support for newer CPUs (Intel's Kaby Lake and above, AMD's Ryzen and above). In addition, using newer CPUs in Windows 7/8.1 causes Windows to disable Windows Updates which is a massive security risk. There's patches/hacks around this I'm sure, but there's other likely possible issues involved. The security implications alone would cause me to recommend the alternatives, which does include upgrading to Windows 10.
Also with the newer hardware issues aside, the way I see it, Windows 7 only has a year left of extended support (ends January 2020) so you'll have to end up having to make a decision a year from now: 1) stick with Windows 7 until the absolute end which means zero security updates, which I wouldn't recommend in this modern world (especially if you plan on upgrading your hardware), 2) upgrade to Windows 10 (yes, you can still update to Windows 10 for free if you have a Windows 7 or 8.1 license) or upgrade to Windows 8.1 (you'd have to get a 8.1 license, which Windows 8.1 has extended support until 2023) though the issue with using newer hardware/CPUs remains the same or finally 4) move to a different operating system like a Linux distro.
I guess the 5th possible choice would be, since you're using the Professional SKU, would be to pay Microsoft money to receive Windows 7 updates for three more years, but then ultimately all you'd be doing is buying time. It's not worth it when you can't even use your newer CPU to its fullest.
Honestly, Windows 10 isn't that bad.