Thanks for the tips (especially of the more historical variety). I am going to plump for the three DG sets (not all at once!) - Kubelik, Bernstein and Abbado and pick up the Mengelberg #4 as that sounds right up my street and I really want to hear the 1938 Bruno Walter fragment of #5 at very least. Anyway. Appreciate the time and the thought. Cheers.

The #4 I forgot to mention is a bit off the radar but it has the Toronto Symphony under Oundjian (no, me neither) and features the brilliant Barbara Hannigan in the final movement. I would at very least recommend just downloading that 10 minutes worth for 79p.