Curiously in the past 24 hours two different entities have effectively asked the same question - "given development funding, can the Perl core be made faster?"
Having spent a couple of years trying to benchmark, profile and accelerate the core, generally with no measurable impact, I'm coming to the general conclusion "no". Of course, there are specifics - there are still some algorithmic wins to be made in the regexp engine, and Yves' recent work on these is very welcome. In turn, there are improvements that can be made to the regexp engine's optimiser (the code that attempts to avoid even calling into the engine itself). But apart from that, my considered opinion after banging my head against the problem for so long is
I reserve the right to be proved wrong. Only working proofs will be accepted.