"Bargain" shopping for Explorer II 16570 - Help me decide which one to go for.

[Auragentum]

So I have been looking to supplement my small Rolex collection with the discontinued Explorer II with white dial. Recently picked up a gorgeous YM but still haven't forgotten about the polar explorer which I have been eyeballing for quite some time.

So I am in a situation where I managed to track down a BNIB random series Explorer II from an AD, which I can purchase at what I consider a very attractive price - the equivalent of approx. $5,700 USD at today's exchange rate.

Alternatively I have a private but reputable seller at hand which has offered me a mint 2007 Z-series (with engraved rehaut) including b/p at approx. $4,400 USD.

Now for some of you it may be a no brainer as to which to choose, in which case I would appreciate you stating the obvious

But which one do you think gives the biggest bang for your buck? Btw, I plan on keeping it, but selling or trading it in for something else could happen in the future (2-3 years time).

So let me know... which one would you get and why?