UPDATE
Windows 7 is a no-go on the ASUS B250 motherboard. The only image I have, however, is the 48-in-1, Windows 7 with many versions (it's always worked well for everything else in the past). So Windows 10 it is... and I was able to get a W10 pro key for just 5 Euro ($6.38 in the US). It activated no problem and was instantly emailed to me... gotta love eBay. So we'll stick with Windows due to its versatility to easily switch algorithms as Ethereum mining is becoming less profitable by the day!