the calibre of 5101P is a new creation from Patek and just been lauched about 2-3 years. I was told these are made exclusively and less then 10-20 a year, and their accuracy have to be endorsed by Philippe Stern/Thiery Stern himself.
I was lucky to see one in person. It is a big watch but the feeling on your wrist is sublime. A Malaysian friend of mine bought one in Aug 2006 and I bet he is very plesased indeed as 5101P keeps on appreciating in value almost by 30% now. So get one if you can.
Larry