The ATPro can be used for gold detecting, considering it has a lower frequency than the ATGold, and in theory that should make it less susceptible to ground mineralisation, but not as hot on the real small nuggets. The biggest issue is the ATPro not having an audible threshold like all the other gold vlf detectors have, so you may completely miss any faint or small targets. The Whites MXT also runs about the same frequency and has been successful on gold worldwide, but it has an audible threshold in prospecting mode.
If you want to do beach detecting as well, both the Fisher Gold Bug Pro and Teknetics G2 will ground balance all the way to salt, making them very usable on wet sand, and great on fine gold jewellery like chains (same detectors, but with different coils and shaft setup). The White MXT Pro has also been successfully used on beaches, and has the same proven ground tracking/ground grab setup as on the GMT.
In saying that, as mentioned above, gold detecting with a vlf detector these days can be a real chore, with many areas cleaned up with pulse induction detectors, so be prepared to learn the detector inside out, and put in plenty hours of detecting.
Also maybe give the Minelab X-terra 705 a look at as well.