I've been following the forums a lot lately and people are really complaining a lot of Sierra and how poorly it's running on their systems. I wanted to share my experience with it. I've updated a MacBook Pro 15" 2010, and 2 iMac's both from 2010. All three run great with no issues. The MacBook was the clean install and the iMac's were upgrades. I had the pleasure of doing a clean install of Windows 10 Pro on a Lenovo X220 laptop today. I was shocked how terrible the system ran, wow. I'm talking about just basic web browsing. Ironically the X220 has a faster CPU than the Mac's I upgraded with the same 4GB of RAM. So if you think Sierra is running poorly on your older Mac, you should be happy you're not upgrading to Windows 10 on a older PC. I installed Windows 7 Pro on the X220 and it ran great again.