So I handed the car back on Thursday night and collected my very shiny and spotlessly clean 149000 mile f10 530d. Some comparisons with the 1700 mile 540i xdrive will be obvious here and others maybe less so. My car is an SE on 18inch wheels and the 540 was an msport on 19s. In terms of ride quality, the 540 was good but noticeably harder as you would expect. My car also has adaptive dampers so this also helps. Whilst far from objectionable, the 540 was not as comfortable and I definitely noticed bumps and potholes more. This is probably in large part due to the state of our roads but I'll not go there! Noise and general refinement are on a par with the f10 I would say. I find the f10 to be very well built and a very refined car anyway. Even after 150k miles!
Interior wise, the 540i was high spec with a leather dash and high grade leather. Layout of everything was instantly familiar and not massively different. Jumping straight back into the f10 there were some differences. I would say the g30 is a bit more roomy inside but not quite as cosseting as the f10. I find the cabin on the f10 exceptionally good and feels I suppose a bit like a cockpit in terms of how close eveything is. I prefer the idrive screen being part of the dash in the f10 as opposed to the seperate screen on top of the dash in the g30. That being said, the idrive in the g30 is streets ahead of mine. I have CIC in mine and not NBT but it also seems a big step up from the NBT in my mates 2014 335d. All easy to access and noticeably hidef screen. The instruments on the g30 are also excpetional. All TFT and very modern.
The biggest test was obviouslt the engine in the 540i. What a weapon! The 530d is hardly a slouch with a lovely fat slug of torque across the majority of the rev range but there really is no comparison. The max torque from the 540 is there virtually from tickover and the power builds in a very linear and predictable way all the way to the 7k rpm redline. God is it fast! Especially at national speed limit speeds. It would be very easy to get into a lot of trouble with this car and I think there would be very little on the roads which would see which way it went. I never got tired of planting it and listening to the noise. Fuel consumption wasn't great but then I was hardly driving sympathetically!
Overall, seriously impressed with the car and a worthy upgrade to what i think is already a superb machine. Would I pay 60k for one? No even if I was in a position to do so but I would consider a used one in a few years. I would love to try the new 530d actually to see how that compares.
Hope this is useful to those that requested a review. Happy to answer any other questions.