I might be able to help here
I have an E60 530d.
On a casual run, I get early 40mpg mixed motorway / A road. Keeping a firm fix on the speedo on the motorway I can achieve late 40s or even 50mpg. This obviously drops the minute you leave the motorway.
The E60 was lifecycle improved (LCI) in April 2007 but this didn't reach cars in the UK market until 57 plate. I have seen one LCI on an 07 plate. Equally, I have seen one pre LCI on a 57 plate (although these are usually special order cars). General rule of thumb is 57 plate onwards equals LCI.
The 525d is also a 3 litre straight six (LCI) same as the 530d but has pretty much similar fuel economy although the 530d is quite more powerful. The pre LCI 525d was a 2.5 litre 177bhp. The LCI 525d is 197bhp.
2009 plate saw the addition of the CIC hard drive based iDrive. Better by far over the CCC drive unit I have (as Fox will be able to add).
LCI offers better interior, slightly different layout and different bumpers / lights on SE models. M Sport models offers the same as above bar the bumpers (which are the same on both LCI and pre LCI).
There was an issue with swirl flaps on the 6cyl diesel units, but this was on early cars and was resolved in 2007. The LCI diesel (of the 530d) recevied an engine enhancement. Pre LCI was 218bhp, LCI was 235bhp. There was also a run of 231bhp 530ds available too but these don't seem that common 2006-2007 production only.
Auto boxes were improved on the LCI models too.
Happy to answer any questions. Plenty of cars on Pistonheads or BMW AUC to look at.