I love Nomos and while their automatics are still a nice value buy, I think their handwound models are even better buys. My favorite Nomos remains the 35mm Orion or 35mm Tangente.
If you must have the automatic, go for the no date one as imo the datum ones look weird with the date at slightly smaller font than the other numbered indices. Also, be aware that Nomos does not have a traditional quickset date (you will have to wind time past 12am, wind back a few hours, wind forward again). For these reasons, I don't think the date complication is worth the $600 premium.
The PO chrono is nice but its a big big thick ass watch. Its just not very versatile.
Anyways, if it was my money, I would probably get a used Omega Speedmaster Pro 3575.50 and a used 35mm Nomos Tangente/Club/Orion handwound no date for about $4000 to $4500 total.
If you are really wanting a IWC though, this double chronograph off ScreaminAsian's link is very interesting and IMO priced nicely.
http://forums.watchuseek.com/f30/fso...c-1181442.html
Not a huge fan of IWCs with non modified ETAs (yes I know they supposedly finish these anyways, but if there is no added complication and its all hidden away behind a solid caseback, whats the point) and the 8days ones are slightly above your budget even used.