DILEMMA ! cheap 16520 or new 116710 ?

[BASSETHOUNDS]

It must be sods law , I'm about to pull the trigger on a GMTIIc since last saturday ( I have been shopping around to get one from the US with the favourable exchange rate at the moment ) but I thought with some hackling I might get close with a "national" watch , no hassle with customs or imposing a cousin to wear and walk it in .
I just received a call from a good buddy , that remembered me saying once " If you sell your 16520 one day let me know " He needs cash TODAY and lets me have it for 7000 EURO . Mint T-reg white dial , overall good condition with 2005 service documents ( no original doc , no original box ) . What should I do ? I have a F-reg 116520 white dial
Option 1 :Buy and keep it , but that would mean no GMTIIc for a while
Option 2 :Buy and sell it again
Option 3 :Buy keep it and sell 116520 to buy 116710

What would such a 16520 fetch net nowadays ( I have no experience with "flee-bay" and I believe that there are a lot of fees and PayPal on such items .
I must act quickly