I know it’s a mad subject but hear me out…

I currently have a 4.2 supercharged l322 on lpg. With the cost of lpg sky rocketing and availability reducing, it’s costing me about £75 to get 230miles on lpg.

My question is - with mixed driving would that kind of bang for buck be achievable on a 5.0 supercharged l405? Current stable:
2006 BMW M6
2007 4.2 V8 S/C FF
Gone:
2002 4.4 V8 FF

28-32mpg motorway cruising

11-14mpg stop/start city/urban

19-21mpg mixed

That's probably about right, though I'd regard 28-32 as pretty unusual, maybe downhill with a strong tailwind. It also depends on things such as tyres, whether it needs a service etc. For comparison yesterday I put £116.27 of Shell V Power in mine (69.25 litres) and that moved the indicated range from 99 miles to 425, that being on summer tyres with a high proportion of motorway mileage at steady 70mph. I always use E5 super unleaded. Only Range Rovers since 1988

As already said it varies quite a bit depending what you're up to (speed/towing/stopstart/etc). But for comparative numbers ... my first 4.4BM V8 was ~17; the 4.2SC ~19; the 5.0SC ~21; the 5.0 SVO ~23. Mike - MPx

2017 5.0 V8 Supercharged SVAutobigraphy Dynamic SVO Palette Grey (2021-...)
2012 5.0 V8 Supercharged Autoboigraphy Orkney Grey (2017-2021)
2007 4.2 V8 Supercharged Vogue SE Tonga Green (2012-2017)
2002 4.4 V8 Vogue Bonnatti Grey (2008-2012)

RRV8SC wrote:

28-32mpg motorway cruising

11-14mpg stop/start city/urban

19-21mpg mixed