Not wanting to dampen anyone's fireworks, but my experience was that the trip computer was around 12% optimistic on average which means the 46.3 was most likely around 41.5 in reality.
Using brim-to-brim measurements, my 265bhp 7G+ car over 34,400 miles averaged 38.07mpg, with a best tank at 42.89mpg and a worst tank at 34.86mpg. Most of my driving is on fast A- and B-roads with some motorway driving, but very little town driving.
For reference, with the same usage pattern, my E63 BiTurbo has averaged 24.18mpg which is pretty impressive imo - especially as I drive it harder than I did my E350CDI.