Will it hurt putting Royal Purple 75w-90 gear oil in my car's rear diff?

My car calls for 80w-90 oil, and I tried to see if Royal Purple makes that weight of oil, but apparently not as far as I've seen from their website. I know Royal Purple is really good stuff... and expensive... but the cost doesn't bother me. Just wondering if I put that in my rear end with the correct friction modifier, if that will affect it adversely due to it being a slightly thinner weight.