So, I finally did enough reading and got my head around this UEFI and GPT business. It's wonderful. You can now have as many partitions as you like without the 'work around' of extended and logical partitions! The boot process is no longer held together with sticky tape and string but feels solid and can be managed.
I presently have Mint, openSUSE and elementaryOS installed. By making sure the user(s) in each distro have the same UID and GID all my documents can be accessed and modified from within any distro, so if I decide I like one better than another changing over is easy.
I did a fair bit of reading but by far the most useful guide was here.
https://www.happyassassin.net/2014/0...lly-work-then/