Dunc,
I fly a 1973 E model and on average budget for about 100 litres per hour. This is a fair mix of short hops (20 - 30 mins) and longish cruises (2 hrs +) at FL100.
I have found it to be very stable for instrument work and, all things considered, a great plane to fly.
One point to watch out for if you're thinking of buying one - the maintenance bills can be very high, particularly on the earlier models (most of which are showing their age....
)
If you've any questions about it just drop me an email