Not sure what you mean by 'efficient', they are faster for sure (amazing memory bandwidth thanks to on chip memory), but to my knowledge they would be the same for amount of data stored. So that same think pad will likely be faster at tasks that need 24GB for example, highly depend on the use case as always.
Memory requirements for general-purpose desktop usage usually don't come down to a single task with a large working set that needs to fit in RAM in its entirety. It's more often a matter of the aggregate memory usage of many tasks, which means that in practice there's a wide gray area where the OS can make a difference, depending on the effectiveness of its memory compression, swap, signalling memory pressure to applications, suspending background tasks or simply having fewer of them in the first place.
