Like I said, 40 MIGHT be ok if you're in a hot climate and it's summer. 50 is no good, way too thick.
Here's the issue, the thicker the oil, the harder it is to pump. The reason anyone only ever sees 60-65 PSI on the oil pressure is because there's a relief valve built internally. So, when the engines cold and the oil is thick, the pump builds to 60 and then 'vents' excess pressure. This means that the oil is taking a long time to reach the top end, the camshaft, lifters, rockers, valves. The longer you see the oil pressure pegged like that means that the oil is restricted. You do want some restriction but not too much.
Thinner oil means it flows easier and provides less restriction so fresh oil reaches critical areas quicker. Thicker oil takes much longer, especially when the engine isn't up to operating temp.
The other side to this is that if you have a really worn out engine and the clearances are much larger than normal, adding a thicker and more robust oil may help keep PSI higher which can mean a more constant flow. This does not help the engine as the damage is already done, it simply masks the problem.