The consensus on what is a safe number is going to be .050" for an aluminum rod and .040" for a steel rod. The reason being is you need to have some "wiggle" room. Things many don't account for is skirt design, and piston to wall, as well as ensuring the stroke is equal on all cylinders and the type of material used for the rods etc. So I think you will find those to be the most common numbers thrown around out there.

I have run as little as .040" aluminum block aluminum rod with no issues on my sruff. We run the Vette even tighter at .033" with an aluminum block and rods too at 10,000rpm. But alot of things have to be perfect to get away with that tight of a clearance. When trying to get to 18-1 compression you have little choice but to push things a bit.