Your current tax is now 195 (or is it 205), same as my 1998 3.0

3.2 will be 245 (bought one a couple of weeks back).
My TD was a prefacelift, so was same as my 3.0l.
3.0 v 3.2 - similar mpg and performance, nothing between them. Reliability wise, both have their common issues. DBW v6 pop their coil packs at around 100k, non dbw v6 kills the dis/leads (that said, my 166k MV6 is on original dis and leads). 3.2 suffers precat issues, 3.0 have icv and egr to stick...
TD mpg unchipped and with autobox is poor - I averaged high 20s. Chipping dragged this up to low/mid 30s with the chip I used. Obviousy more on a run (chipping a TD also fools MID, so you have to test MPG the old fashioned way). If I had another TD, it would have to be a manual, and chipped. Personally, I prefer the 2.5TD to the 2.2DTi, smoother, better power delivery (when chipped, poor unchipped), less highly strung. When the TD goes bang, though, it tends to do so in style...