There are just so many factors to Windows mining like this between BIOS settings, cpus, memory sticks, and old school Windows 7 pro. You should look at Windows 10 to possibly get an apples to apples comparison since Windows 7 is EOL. If you have a couple of spare flash drives, giving HiveOS/Linux a shot in the short term might help even things out?

Anyway, yes, Nicehash supports KawPow natively. You'd just need to let it benchmark assuming you're running Nicehash.exe.