[JEM]

The Jag's 390HP ought to be worth about 320 at the wheels - you can customarily assume 13-15% losses through a manual transmission, a bit more through a conventional hydraulically-operated automatic.

Your gas mileage numbers are quite good, far better than anything I've ever seen with our comparable household fleet ('98 540iA averages 17mpg, '00 M5 averages 17mpg, '02 Audi S6 Avant averages fractionally under 17mpg, those numbers are based on 50/50 highway/local and on oxygenated 91AKI California crap gasoline, if you're somewhere fortunate enough to get real gas you might do a bit better, on its Euro Delivery trip way-back-when the M5 averaged 21mpg on German and French 98RON non-adulterated real gasoline despite cruising at 130-150 every moment I could manage it.)