Rupert
Wettable sulfur is a better option and easier and cheaper to obtain. Lime sulfur is another option but it knocks the beneficial insects and mites around more. Another option is to go biological and release some predatory mites but perhaps a bit expensive and over the top but it looks like you're verging on semi-commercial there. Planning on setting up a stall selling fresh hops at the albany farmers market?
Neem, while often quoted as the new magic bullet of insecticides, it's never really gone anywhere. Results haven't been outstanding for many pests, and it still seems relatively expensive. Perhaps it's worked for you and could be used for other pests. Sulfur is widely and successfully used in many australian industries for spider mite control.
Spider mites typically attack stressed plants or occur as a result of insecticides being sprayed that knock out their natural enemies and the mite populations surge. They love hot dry days. Even just finely spray blasting the foliage of plants with water regularly can knock back a spider mite population substantially. In your case it looks like hot dry days may have cranked up the mites as your plants don't look very stressed.
Lochy