Performance costs of various PL languages

We are currently using pltclu as our PL of choice AFTER plpgSql.

I'd like to know if anyone can comment on the performance costs of the
various PL languages BESIDES C. For example, does pltclu instantiate faster
than pltcl (presumably because it uses a shared interpreter?) Is Perl more
lightweight?

I know that everything depends on context - what you are doing with it, e.g.
choose Tcl for string handling vs. Perl for number crunching - but for those
who know about this, is there a clear performance advantage for any of the
various PL languages - and if so, is it a difference so big to be worth
switching?

I ask this because I had expected to see pl/pgsql as a clear winner in terms
of performance over pltclu, but my initial test showed the opposite. I know
this may be an apples vs oranges problem and I will test further, but if
anyone has any advice or insight, I would appreciate it so I can tailor my
tests accordingly.

Thanks,

Carlo