I must admit, like RichardK, I was skeptical about the benefits of using elsifs where the logic short-circuits with returns anyway, and immediately tried switching from your:if( cond ) { return x; } form to the statement modifier form: return x if cond;; and ... it made no difference. elsif still won out.

So then I looked at -MO=Deparse,-x9 to see if if/elsif/else chains were perhaps being converted to some kind of jump table or switch.

But no. They appear to be implemented as (the equivalent of) a chain of nested ternaries, but when I tried coding them that way, they were still slower than the if/elsif/else chain?

I then turned my attention to your rather more interesting innovation; namely (partially) unrolling a binary search. I tried adding another level, and got greater benefit; then another and (reduced, but) still more; so then another; and the benefits ran out :(

My (long and winding) benchmark and results are here:

Many thanks for a) responding; b) teaching me something(if/elsif); c) stimulating my brain in a different direction (hardcoding a binary search).