I was able to use Logic 7 running OS 10.12 Peter, I kept it around in order to access very old (pre Logic 5) projects. The earliest OS for Logic 7 was IIRC 10.3, but I think that changed over the course of development - as you might remember, as and from Logic Pro 7.2 universal binary became important with the arrival of the first Intel Macs. Logic 8 was released in 2007, just prior to OS 10.5, so I suspect the earliest OS it ran on would have been 10.4. No guarantees at this stage as to the validity of all of that! Not sure if this is your concern, but any projects from logic 5 onwards should be openable in Logic Pro X, albeit if they are pre OSX/Audio Units then there may be some issues with recognising plugins you might have used back then.