[Brion Toss]

Hello,
The question was, I believe, whether a keel-stepped mast is "stronger" than a deck-stepped one. The answer is no. However, a keel-stepped mast is definitely stiffer than a deck-stepped one, and that, as Ian points out, is information that any engineering manual can confirm. So if you want to save weight, and there's room below, basically keel-stepped is the way to go. If you want to raise and lower the mast, or play with extremes of rake under way, or want to build a boat more cheaply, or any number of other considerations, then go deck-stepped, and up the scantlings accordingly.
Fair leads,
Brion Toss