Hi,
The 2.2 swb will probably return around 25mpg so that isn't going to be better for economy than the 2.3d. The dash clock problem is a known issue and can be repaired with a soldering iron if you have one/feel competent to do it. If not there are others around that may be able to assist. If its economy you need then I would look to stay with the 2.3d.
If you were looking for something smaller and more economical then the "nirvana" would be a 3.2v6 SWB on gas/LPG. this would give you better MPG ( around 28-30 )and loads more power. The additional benefit ( and where you gain ) is that LPG is only 0.65p a litre so you would effectively get nearly double mileage out of it for the same cost.
The 3.2 swb are fairly rare, but economy wise you could go for another lwb 3.2 on LPG and get the same benefits. I suppose its just how much you want the smaller car?
I don't really know the diesels that well, I am sure someone will be along to advise accordingly who can confirm the above or shoot me full of holes
