I dont know about larger hoses to the cooler reducing viscosity. I would imagine it would tend to increase flow, and aid cooling, (which would increase viscosity). Larger hoses would be less resistance though, irrespective of the viscosity of the
oil, and maybe that helps, especially pushing cooler
oil out of the cooler and back into the engine.
I have a cooler with -10AN, and I know most people are running -12AN these days.
I was told the following, with regard to lowering the load on the distributor. This applies to a street driven SBF stroker:
1) Don't punch it until your
oil is warmed up > 80C/175F
2) Use a thermostat in your oil cooler setup. Mine is set pretty high, 112C/232F I believe.
3) 10W-40 is what Keith Craft recommended to me for my motor. Others have told me to avoid 20W-50 for normal street use.