Hi. We have all 3 types of engine in our family, my parents have a 525d that I drive regularly and I've a 530d, I previously ran and still have a tds, albeit in E34's.

I find the 525d noticeably quieter than the 530d and it drives me insane that I own the noisier car! The former hums from cold start and could easily be mistaken for a petrol, whereas mine or any I've heard never could. I typically got 47mpg at minimum from the smaller engine, rising to 54mpg on a long haul, whereas the 530 just about gets over 40mpg everytime, rising to 47 on a long trip. The dash econometer is a bit more optimistic in the figures it gives.

The larger engine has noticeably more power in give and take overtaking situations, neither engine pulls in the higher rev range as good as the older tds. That used to give 37mpg by the way and hit 40 just the once in my hands. The annual road tax on the 530 is hard to swallow at €1500, in fact I'm staring at my renewal notice right now.

When it comes to running costs, I find that whatever gains have been made in fuel economy are equalled by maintenance costs. the 525d is about 25% more economical than the 525tds yet has components such as an injector loom for instance that eventually becomes brittle and has to be replaced, such an item doesn't exist on the older car! The same goes for 530d.

All things considered though, I'd be one of the few that's steer you more towards a 525d. It does 95% of what the 530d will do, sounds sweeter, drinks a bit less and cost €400 a year less to tax.