Well...
My own rules of thumb are quite lower than Dougal's!
He says 30L annually from a dwarf tree, this would mean about 55kg of apples - this is quite high yield! Probably attainable on a very good year, but I don't think this can be considered as an average long term yield - at least in the sort of terroir where I live.
I usually use much more conservative numbers as average yield, like 50 kg of apples from a standard tree and 25 kg from a semi-dwarf - but this is an average taking account of the off years. For example, 50kg from a standard, at 8m x 8m spacing, would give 8 tons per hectare, which is pretty representative of a traditionnal orchard on an average year.
On a semi dwarf, I usually use 25 kg per tree, times 500 trees per hectare, which gives 12.5 tons per hectare, again a quite representative number.
Naturally, with fertilisation, rich soil and ideal climate, it is possible to get higher average yields - but often apples from such higher yields won't have the same quality for cider...
Claude