Imho the Benchmark subrutines all give back time in wallocsecs, if cmpthese(); works diffrently you can always wrap it inside timethese(); or another sub that returns time in wallocsec.
This is what perldoc Benchmark tells you about a possible modification of wallocsecs:
:hireswallclock
If the Time::HiRes module has been installed, you can specify the
special tag ":hireswallclock" for Benchmark (if Time::HiRes is not
available, the tag will be silently ignored). This tag will cause t
+he
wallclock time to be measured in microseconds, instead of integer
seconds. Note though that the speed computations are still conducte
+d in
CPU time, not wallclock time.