Stopped in Sheffield today by an Exige owner - he asked what the oil consumption on my Exige was? - I use approx 0.5 litres per 1000 miles. He stated that he uses that every 500 miles.
Change mine every 3000 miles
Apart from the obvious worn rings it could be that the car never gets warmed up properly, its a side effect of having forged pistons, the oil will blow past the rings until they have warmed up and expanded.
Short journeys will give you that sort of consumption.
You also lose more at higher revs. On a good trackday you may also lose a litre.
Yours sound about right to me.
Ian