Are any used ThinkPads powerful enough to run Windows 10 smoothly?
For $1000 you can get a new Thinkpad X1 Carbon(Gen3). Lighter than a Macbook Air but specs comparable to a Macbook Pro. I got one recently and have dual booted Linux and Windows 10 on it.
Yeah, that's no problem unless you start looking into the <$200 or maybe <$300 range.