The "technical" answer is "whatever you can find bearings for." I believe .030 is accepted, some cranks maybe older engines may have had .040
For some special "stroke" builds, different rods, etc, some cranks have been turned a LOT more than that. Found this post in a similar discussion:
"Before 350 journal sized stroker cranks were available, it was common practice to turn a
SBC 400 crank .100" under when building a 383".
And someone corrected:
"Nope. Turned .200, not .100.
400 main size is 2.65", 350 main size is 2.45". .200" different"
