I took the 15.6 from tyrefitters profile signature - I agree my 4.2 only did 13 mpg & that was driving like there was a fuel shortage  16MY Estoril Blue SVR.............
17MY Autobiography Dynamic - Corris Grey - WOW.
14MY Autobiography Dynamic - SDV6 - Fuji White
12MY Autobiography - SDV6 - Santorini Black - Dual View - Rear Entertainment - Sunroof.
12MY Autobiography - SDV6 - Orkney Grey - awesome ;(
2005 Java Black - 4.2 V8 Supercharged First Edition- will never be forgotten ;(

I’m thinking supercharged 5 litre !!!
I am going to use an average of 10mpg 2006 RRS Supercharged 4.2 HST muthuaflecka!

10-15 as an average me thinks but you don't buy them for fuel economy

I get an average of 17l/100km (17mpg) in my 2010 TDV8. The car does two 15km (9.3 miles) trips per day with a 7-8 hour gap between them (two school runs).

The 15.6 is mainly town driving is sport mode making a lot of noise with the window down.I have yet to go on a long run.

Andy Andy.
21 Ford Ranger
Gone but not forgotten
Focus RS Red Edition
2015 RRS AB Fuji.
2014 RRS SC Santorini
2016 VW Amarok
2014 RRS AB Fuji
2012 RRS Red Edition Fuji
2015 Nissan Navara
2012 RRS SE Santorini
2008 RRS White
2007 RRS Santorino

2008 TDV8 over 2 years ownership and covering a total of 28348 miles average is 25.12mpg. not much motorway, some 40 miles trips across country, and often short trips to town of 4 miles or so. (assuming my maths is OK ) Robin
2008 Range Rover Sport TDV8
Gone:
Jaguar S-Type V8 4.2 Sport
MGZTT 190 2.5

It will cost you more like for like but honestly, doing that little mileage, I would ALWAYS go for the petrol variant.

Even diesels aren't exactly cheap to run and ;et's face it = if economy were the main factor you'd not be considering a RRS in the first place!

Get the 5.0 SC, turn off the MPG display & drive with a constant grin on your face even if it is coupled with a hole in your wallet

The man-maths missed out the additional VED payable on the S/C over the TDv8........ not sure how much more it is but the CO2 emissions of the S/C are quite a bit more than the TDv8. For the annual miles though as stated above the petrol is always better for low miles journeys. 2020 Pangea Green 1st Edition D240 New Defender 110 is here and loving it
2018 Melting Silver Mini Countryman PHEV - soon to be replaced
2015MY Corris Grey SDv6 HSE Dynamic, the best car I have ever owned, totally reliable only a cou0le of rattles in 3 years, now no longer in my care
Also in my garage is a 1996 TDi300 Defender 90 County HT made into a fake CSW

My14 SC is £535 a year to tax

Andy. Andy.
21 Ford Ranger
Gone but not forgotten
Focus RS Red Edition
2015 RRS AB Fuji.
2014 RRS SC Santorini
2016 VW Amarok
2014 RRS AB Fuji
2012 RRS Red Edition Fuji
2015 Nissan Navara
2012 RRS SE Santorini
2008 RRS White
2007 RRS Santorino

Good point Tim. My 2008 TDV8 of course gets clobbered with the full wack presumably you are saying that the later TDV8s do better on CO2 emissions. Robin
2008 Range Rover Sport TDV8
Gone:
Jaguar S-Type V8 4.2 Sport
MGZTT 190 2.5

Having just taxed mine yesterday, I can tell you the L320 is £555 for 12 months. I pay mine monthly so it increases to £582.75 in total. Ouch... 2019 5.0 SC SVA (Current)
2012 5.0 SC AB. Sadly written off by a campervan
23 plate Focus ST (Current)
1942 VEP Ford GPW Jeep (Willys) (Current)
1943 Whites M16 Halftrack (Current)
16 plate Eurofighter Typhoon, 2 x Eurojet engines with 20,000lbs thrust each. 1380mph

Ouch. In February I paid £535. Something tells me they don’t like older diesels Robin
2008 Range Rover Sport TDV8
Gone:
Jaguar S-Type V8 4.2 Sport
MGZTT 190 2.5

Sorry, should have said mine is the SC Petrol not Derv 2019 5.0 SC SVA (Current)
2012 5.0 SC AB. Sadly written off by a campervan
23 plate Focus ST (Current)
1942 VEP Ford GPW Jeep (Willys) (Current)
1943 Whites M16 Halftrack (Current)
16 plate Eurofighter Typhoon, 2 x Eurojet engines with 20,000lbs thrust each. 1380mph

Brit Plumber wrote:

Having just taxed mine yesterday, I can tell you the L320 is £555 for 12 months. I pay mine monthly so it increases to £582.75 in total. Ouch...

Same for me. Much less painful paying monthly though  Steve.