I do very similar miles to you in my R for my commute and then some on evenings/weekends, I fill up every 4 to 5 days at £70+ a time. It works out at approx £450 a month on petrol give or take. That is the first time I have actually added it up, and it is quite sickening to see that figure. Looking at that would I opt for a diesel next time, maybe, as you are doing around 15,000 a year just commuting, add a few personal miles to that and you are doing best part of 20K a year and thats alot of petrol. Wish I hadn't bothered to work that out, just glad my wife doesn't come on here.