Final numbers from my cross-country drive.
And there were loong stretches at mileage-killing high speeds (and the usual construction jams):

 

Your figures agree much with mine. But doesn't it vary a lot with where and how we are driving? If I stick to UK speed limits on Motorways I can get 31mpg in flattish country. In busy town traffic with the occasional burst of throttle to get through lights before they change from orange, I can get as low as 19mpg. Over a month of my normal usage, which includes all the above, I get 26mpg.

Anyway, it's worth every penny, most of which in the UK is tax of course.

 

My wife's daily driver is a Volvo S60 T8 plug in hybrid 2.0 litre and gets 3litres/100km or 79MPG.
Goes faster than the 5.0 XKR! Her Volvo is quick at 4.3sec to 100km/h. I don't feel guilty driving the XKR as a weekend toy.

 

In US MPG, I get about 20mpg but Im not doing real highway, but city and backroads and come on, that ain't bad for what these are! Best was 70mph on flat land for about 270miles and I got 26 real mpg (got gas before and after the round trip).

My VW Jetta on the same roads gets between 38 and 42mpg winter and summer US mpg; on diesel. Definitely no 4.3s to 100kmh, more like 8s to 100kmh and that was after the tune lol.

 

Top Gear Claim 4.6sec for the non Polestar, 4.4 for the Polestar.

https://www.topgear.com/car-reviews/.../first-drive-0

Where the XKR comes in at 4.6, I'd imagine with a few mods that could be bought down to around 4.3 quite cheaply.

https://www.evo.co.uk/jaguar/xkr

Does your Wife have the Polestar Version?

 

A snapshot of your "average speed" would tell us a lot too for that trip.

 

Well, sure, it's mostly (95%) highway on the trip. However, much of that was at well above 80MPH and you can just feel the gas draining. At a sustained 90MPH I've gotta be going through 5 gallons an hour.
In my normal in-town, stop-n-go driving I get 17, so this was a revelation.

 

Yeah for sure.

I've noticed even if most of your driving is highway, just a little bit of city driving will lower your average speed by a good amount.

I'm not sure how its calculated, but it seems much more weighted towards city driving. So with a large amount of miles driven, and an average speed above lets say 55mph, you can get your true 'highway' mpg.

It seems 55-65 mph is the most efficient. However, I could never willingly drive that slow on the highway!

 

but its just so fun when you keep to sport mode and depress that pedal. So for that reason I don’t think I’m going to monitor my mileage too closely

 

We only get the Polestar version of the plug in hybrid down under.

 

I too get that just driving around town (22-23mpg). My last 400 mile drive a couple months ago yielded nearly 25mpg, and I am not easy on her.