I think I mentioned before my SRT averages around 23 MPG and that was a shock after the MX5 but I love the so I'm prepared to put up with it.
Just to give you a reality check it cost around £83.00 to fill from empty and you will get around 325 miles.
If you want economical buy a 2.0 Z4 but you will just be one of many rather than one of very few with a Crossfire
you can go off people real quick!! that's what I get from my na - that being said though I'm sure I go tmore out of my first XF.
Back to the ones on offer - for me it'd be the 05, they're not too far apart in price and that cargo cover is pricey!!! That being said as always buy on condition and what instinct tells you when you see them both