Buy the $600 GP. When you find all those other better deals, buy them and re-sell the one you have now at a hefty profit.
I was too cheap to buy a nice 4 inch 70's blue speed six last year for $400. My, friends, told me that price was alittle high. Eemmhhmmm. After a dozen gunshows guess what I havn't even seen much less buy at any price?
Some 2 years ago the LGS had a 80's 4 inch ss Service Six, 95%, at $600. A dozen tire-kickers came in told us were were smoking something. Result...next day it left the shop at full price. Who's smoking something now?