Driven: The Alpina B5 is a truly amazing car. 447Kw and 800Nm, yes eight hundred of Sir Isaac's finest metres! Combined with X-drive it has a claimed 0-100 time of 3.5 seconds and I don't doubt it. Interestingly this pushes my M4 GTS back to 4th fastest BMW for the 0-100 sprint after the M760iL, F90 M5 (5th if you include the M5 Competition as a seperate model) and Alpina B5. On a dirty road I stood on accelerator from a stop. It just launched with a spilt second chirp from the rear wheels as the X-drive did it's thing and we were gone, rapidly. In my car warm tyres and a perfect road surface is needed to get the thing off the line quickly as you balance the throttle and keep it straight through the wheelspin. With the B5 my 72 year old mother could run 3.5 all day.
Having driven and been driven in the M5 the main differences are the sleeper factor, the noise and AWD, Sports AWD & 2WD modes in the M5. While the M5 is loud and 'farts' in gear changes the B5 quietly burbles. Sink the boot in and you can hear the B5 but it's nothing like the M5. The sleeper factor of the B5 is very cool. To a BMW aficionado like my self the signature Alpina wheels give it away from a distance and once closer so do the pinstripes and front air dam but to the average punter it could easily be just another BMW sedan. Then of course there is Alpina ride, like floating on cloud. A very fast cloud. It could handle a 2 speed powerglide transmission with all that torque yet Alpina saw fit to stick with the same 8 speed auto that's in all 5 series and it's smooth as silk. The interiors on both B5 & M5 are very luxurious with the M5 being more sports oriented as you'd except while the B5 is just calming, comfortable, luxury.
So would I take a B5 over the M5. The smart me would. Unfortunately the smart me goes AWOL the second I enter a BMW dealership so I'd end up with a M5. I'd always be wondering if that was the right choice though, the Alpina B5 is a brilliant luxury sedan.