You're right, the GS450H did cost more new than 535d/E350, hence my comparison with a similar 6-series which was £60k+ new.
I think the differences must be explained with the numbers available.
Thanks for the links, the GS250 doesn't appeal, neither does a newer version of my current car.
I may just decide keep my current car and run it to the ground but thought the high residuals of the current GS450H were worthy of forum comment! I also wanted to see if the dealers were offering heavy discounts off the ticket price on used GS450Hs.