The HD truck steel cranks are heavier weight wise than the run of the mill cast cranks and considered overkill for most streetable Y engines.  But from a strength perspective, the steel cranks are definitely more robust and very suitable in those truck applications where the engines are being lugged heavily.  Another visible difference between the steel and cast iron cranks is in the counterweighting in that the steel cranks have six counterweights and the cast cranks have eight counterweights.  Regardless of the number of counterweights, the cast cranks were still lighter.  The cast cranks are considered to be fully counterweighted and as such, are more desirable from the standpoint that they exhibit less internal stress in high rpm operation.  And depending upon which crank manufacturer you talk to, you’ll find varying opinions on the counterweighting subject.

I did have a customer that had inadvertently supplied a steel crank as part of his 292 rotating assembly for balancing for his ’55 Crown.  Upon asking him about it, he wasn’t aware of the difference in cranks until I pointed it out but because he had already turned the crank and was ready to get his ride together, would go ahead and use it.  His comments after running the car for awhile was that the engine didn’t seem as aggressive during acceleration as the other engines he had with cast cranks but once at speed, the car was a rock steady high speed cruiser.  This simply reaffirmed that the heavier cranks will tend to keep an engine from accelerating as quickly simply due to the mass involved with everything else being equal.