3700 is a two handed. The 920 JLC was an ultra thin movement with an interesting rotor. The PP 240 is ultra thin with a special rotor. It is Patek's reply to a thin automatic and hence more coherent with the original and with the concept of the watch. I feel the 324 is a very efficient, well constructed and probably cost effective movement. But it is perhaps also a bit more generic in its design.
Let me be clear. I absolutely love my 5711 and am very pleased with the performance of my 324. Let's just say 240 is a very special movement that suits a very special watch.
My ultimate Nautilus would be steel, with a 240, no seconds hand and no date... I've gone back and forth between 5711 and 5712 and while they're both wonderful ultimately I think I prefer the uncluttered dial of the 5711. I just want to take it to the next level! Best E.