D40 speed rating

I am currently trying to satisfy our fleet companies specs for a all terrain tyre for my king cab with some grip, they reckon the manufacturers speed and load rating have to be followed but no one seems to make a tyre that is "H" rated with a decent tread pattern, as if I will be doing 210 kmh anyway, they also want to stick with the original size of 255/70r16 which is really limiting anyway, the factory fit grandtreks have nearly killed me about three times this week, any body got a solution ?
then again doing full powerslides on soaked dirt tracks in 4 high with a tonne on the back at about 90 k's is probably pushing it. (just kidding boss)

I thought the rating would be for a loading level as well, and your Navara can put almost the weight of a Barina on a single wheel (700kg).

the problem seems to be that all of the tyres with some decent grip are a lower speed rating than the spec H which is 210 kmh