I can't add much that hasn't been said in the excellent posts above. These guys know their stuff!
I agree with PP though, saving that extra money for a new machine (or a close to new machine with a good amount of warranty left) would be worth the peace of mind alone in the end. It's always a fair outlay for most of us after all so you're not alone here. We've definitely all been there and asked those exact questions
Personally, I spent around five years saving for the GPX5000 (while digging kilos of junk targets in the meantime using a Garrett Infinium!). Initially I was after a new 4500, but the 5000 was just due for release by the time I had the money together so I figured why not save a bit extra and go with a brand new model. Then by the time I knew what I was doing with the GPX, they dropped the SDC!
Gotta love this hobby... :lol:
Also, and no doubt you've thought about this, but do not discount the SDC as another option, particularly if you're new to detecting. The SDC opened old areas where I would never had thought gold was even remotely findable after the GPX's had already been through.
Either way, both machines will do exactly what you need and find the good stuff if it's about, not to mention that will both have excellent resale value if you decide it's not the hobby for you or you decide to upgrade in the future :Y:
All the best and let us know how you proceed with it.
Regards,
Shauno.