Hi Steven, please disregard Reg's comment, not sure if he was having a lend or believes it. Either way it's crap, he knows it, we all know it and I'm sure you're intelligent enough to know it too.
SDC, excellent switch on and go machine with next to nil learning curve. Great on flogged ground, pushings and scrapes etc but limited depth and ground coverage due to only an 8" coil.
IMO a poor choice as a stepping it out type of prospecting tool.
Excells on small gold and a great clean up machine for patches.
4500, excellent versatile prospecting machine with unlimited coil options. At home in 99% of gold field situations from pushings and scrapes to virgin ground hunting. Has a learning curve but easy to master with time and maybe tuition.
Both are excellent and proven machines. It depends on how you want target gold. ie: hit old ground, prospect for new ground or both.
For versatility I'd go a 4500
Cheers,
Steve