If you are going to buy a GPX 6000, Steve Hershbach's is for sale on EBay right now for $4500. He won't steer you wrong on that one. Also, Ron's Detectors Minelab on the Detectorprospector forum has two for under $5000 with more than 2 years warranty. But if you can wait a few more months, Garrett Axioms will be selling for around $4000 and if you are military, take 15% off from that also. They are supposed to be equally or even better than 6K's especially on hot rocks and they have iron disc the Minelabs don't. I have a 6K with a 10x5" Coiltek coil on it, that a great setup too so I am not selling it quite yet, would lose too much. Seems like there may be a lot more used 6K's for sale soon, so far the going price has been $4500 -$4300 - (from reputable owners! SAD!!) on Fleabay, but those guys are also losing 13% on fees from that price, so find a private sale and negotiate with that if you can.
I understand about your secrecy, good idea. Just beware that by posting a new claim, you are also pointing it out to the public... especially since you already made the finds public. I would do the easy work that is easier to hide on it as much as possible (detect the heck out of it and scrape/cover up some too), then claim it just before the harder more easily seen work (drywashing, etc.). you will have to decide which way to go on that one.
Hope it pans out for you, looks like a nice find.