The 7000 is good for deeper larger nuggets with a more complicated interface and is very heavy like Gare said. The 6000 from what I can tell doesn't go as deep but it will find large and small nuggets equally well. The 6000 has a very simplified interface (similar to a Gold Monster) smaller battery and it's much lighter. The instructions say it's submersible to a meter, but when Minelab talks about the 6000 they say it's "weatherproof." Some people say that pinpointing with the 6000 is a pain in the rear. The Literature for the 6000 says that it's more "powerful" than the 5000, but a new 5000 is $4000, and a 6000 is around $6000. Not falling for marketing hype will save you $2000 upfront. If you're diligent any of these detectors will easily pay for themselves, but to get your first new PI with a warranty go for the 5000. If you want a 4500 you'll have to buy used for under $2000 with extra coils. The good thing about the 4500 and the 5000 is there are a lot of available aftermarket coils.