The problem with electic fans in hot weather is that they will only come on when the water is hot enough at the sensor - a viscous coupled fan will always offer some over engine cooling, an engine is cooled by several means, water, oil and air flow past the block/head other components.
An option would be to run the electric fan all the time via a ballast resisor at say 50% when the themroswitch cuts in it will then offer the path of least resistance and run the fan at 100%. That way your engine is always getting air flow over it.
Option two would be to fit another smaller fan say over the intercooler (if your other fan left some room) which can be switched from the cab and more or less run all the time to offer over engine cooling (might want to duct it slightly so it blows more at the engine than down the side.
An additional oil cooler would also help, come out the stock one, into the secondary and set it up so your constantly running fan cools it.
So many things you could do - I would also take the stat out and drill 4 holes in it, so there is ALWAYS a flow of water through the radiator, always allowing a flow of cool water to pass back into the mix.