This was intended to be a question on optimizing outputing of strings. Not when and what to optimize as that's really a different discussion.

Anyways here are the results of your benchmark on my laptop with linux-2.4.18/perl 5.6.1...

build_print: 24 wallclock secs (20.87 usr +  0.08 sys = 20.95 CPU) @ 4
+7.73/s (n=1000)
list_print: 20 wallclock secs (17.51 usr +  0.01 sys = 17.52 CPU) @ 57
+.08/s (n=1000)
              Rate build_print  list_print
build_print 47.7/s          --        -16%
list_print  57.1/s         20%          --
[download]

I suspect there are serous buffering differences from platform to platform.

Adding "$|++" to the top of the script seems to widen the difference between methods by 1-2%.