Not too bad is my bet. I find the older machines (2009-2012) run better in Windows 10 than the most modern versions of Mac OS they support in terms of speed and responsiveness overall. Mac OS seems to be much harder on old hardware than Windows, different philosophies of OS design. Apple is always pushing forward with the latest and greatest stuff, which is great when you are using the hardware for 3-5 years, but beyond that it’s not so good as they drop support for things that were designed for that older hardware. MS always pushes legacy support, sometimes too much, but it is beneficial for older hardware.
Some examples, when Apple dropped OpenGL as supported graphics drivers, older machines took a big performance hit since they didn’t work with the new APIs. Windows uses DirectX with extensive support for older hardware, so it’s a non-issue. Apple’s response to Spector and Meltdown patches also seemed to hit performance far more in Mac OS than what MS did in Windows.