Morels seem to be opposite from some of the other lifters. Their close tolerances need a thinner viscosity. I have ran 5W-20 in them and 10W-30. All-in-all, you need to keep the kinematic viscosity in check as it can vary from oil to oil and there are some oils that will work with Morels at around the 15W-40 range.
I'm not really an exclusive user of any particular oil. I worked for a bit with the Valvoline engine lab, so I'm partial to VR1, but I also use Brad Penn quite a bit. I think a lot of oils are really, really good, and just like anything else, there's more than one way to get to the finish line.
I freshened up a pulling truck engine earlier in the year, that made over 1200 hp at 8500 rpm, and had a full season of pulls on it. I thought really hard about putting the bearings right back in, but on a $45k engine, $300 worth of bearings is a drop in the bucket. I use Brad Penn on that engine.
Here's a set of 8500 rpm 351C rod bearings after some dyno thrashing:
And the mains:
This was ran on Valvoline VR1...bore mic tracks still intact.
I'm not saying all of this to say "my oil is better than your oil", but I'm just saying that I think there are a lot of really good oils out there......Amsoil, Driven, Brad Penn, VR1, etc. I wouldn't mind to use any of them.