General Diesel 2.4, 5 cylinder auto or 2 litre auto

[sunard]

Hi all, currently have a 2.4 auto 2005 xc90 covered 200000 miles trouble free, but getting a bit thirsty now, I cover 20k miles per year. Was looking to replace with a 2014 XC90, but now considering an XC60 2015 Auto. My dilemma is do I stick with the 2.4 in the XC60 which from my experience is bullet proof, will offer about 49mpg combined & £180 road tax; or embrace the newer 2 litre 4 cylinder engine which I believe is coupled with a newer gearbox offering 60mpg & £135 road tax. It gets used as my work van, so speed performance is not important to me, fuel consumption & running costs are, it will be run to 200k +miles, before I change it again. If it wasn't for the rising fuel costs i'd stick with the XC90, its built so well and has so much room inside for carrying tools. The XC60 does not appear to be as solid as the XC90 but then there's a weight trade off & better fuel as its lighter.
So value opinions please on the 2 engines choices? Thanks.