Nah, don't go 50, too thick. I mean usually, when manufacturers recommend a weight, something like 40, they've taken into account the wear over the lifetime of the engine. 165xxx km is nothing. That and you'll find that compared to manufacturer's recommendations, you can usually go to a thinner oil if you go full synthetic due to the better protective properties.

I think Penrite is popular here because it's good value for full synthetic oil and is Aussie owned (and made?). Otherwise, there's much of muchness between it and other Group 4 oils. I think Royal is group 4 as well.