Thanks for everyone's comments. Just installed X3, it opened an old project 8.5.3 FAR easier and with less faff than 8.5.3 itself, and it seemed very responsive and smooth. Looks like a very good DAW - I won't be migrating back for general use for specific reasons (only Cubase can control midi CCs via EuCon for one, and Cakewalk still haven't got a true narrow track view which is essential for very large projects), but this looks like it'll make dealing with my archive projects a whole lot easier.