I prefer manual too, the only difference is road tax, which is 130€ higher than for 2.5V6 , and consumption naturaly.
Price is high even for used cars here but I prefer the devil I know over some beemer or merc.
Im probably going to annoy a few 2.5 and 2.6 Owners here, but given to choice or the two its got to be a 3.0, them few more HP's make all the difference and make the 3.0 so much more drive-able over the 2.5.
Consumption wise theres not much in it when driving normally, its only going to be a lot heavier when your flooring it.
You could also Chip it for under £100, gives it a bit more Grunt at the Top End with a few more Horses, but will increase your economy. My old 3.0 MV6 Manual which was chipped would do 27+ MPG on average spending half that in and out of London Traffic, and around 35+ on a sensible Motorway Cruise, Both my current 3.2 Manuals cant get anywhere near that.