Don't know if this helps at all, but I have a power-steering box on my HJ ute, with what I believe to be larger-than-standard tyres, and it is effortless at low speeds, single finger! Haven't had the opportunity to try it going faster than 10km/h though, especially now as it's in bits!
Best of luck!
Bluey

Just realised I revived a dead thread. Amateur hour over here!