Mojave wasn't a major change from High Sierra so most things that work with 10.13 should work with 10.14, however, in some cases there won't be guarantees (e.g. Note that with High Sierra Apple changed the underlying filesystem, so some apps (notably Apple's older Pro Apps Logic Pro 9, Final Cut Pro 7, etc.) don't work. What I would suggest is looking at the apps you need to run and see if there are issues with any of these newer OS versions. To be clear here: I have a late-2013 MPB, so performance will be different. And unlike running newer iOS versions on old hardware, I haven't seen a degradation in performance with newer OSs. I'd probably still be at 10.6.8 if I could, but I've been fine running what I need to run up to Sierra (10.12). I haven't seen a compelling feature in years. To be honest, the only reason I upgrade my Mac is because I need to to run a certain application (usually something from Apple).