M40d vs 30d

Mrs isn’t convinced by the isofix in the M3 so looking at an X3 m40d

Indo a shit ton of motorway miles so you m40iers relaxxx

Also looking at the 30d… maybe more baby friendly financially/practically ? Seems cheaper to run, gets better mpg, I’ll for sure sneak a decent stage 1& gearbox tune on it to close a bit of the performance gap. Obviously theres still major differences in set up but still.

Anyone owned or driven both? Would appreciate thoughts on whether theres actually a significant difference in how the M40d feels compared with a 30d in normal driving, and whether it’s worth the extra running costs. Could do with a break spending on tyres and fuel

22 plate & below let’s say, not a fan of the newer models