I keep a close eye on prices and if it was any other engine size I could give you a firmer idea from experience. But the 2.8s are in my blind spot as they've never appealed to me so I don't look out for them so much.
But my finger in the air was try at £4,250 and see where it goes. Having just trawled through ebay 'sold for' listings there are cars with half the mileage going for under £4k. If your's was an average 100k'er I'd say £3,250. But you've got all those nice bits and the recent maintenace history and I think that could add between £500 and £1,000 to the value. So I'll stick by the £4,250 punt and say aim for £3,750 which is inline with Tony's £500 advice.