MCE has the parallel_io option which is not enabled by default. This seems like a good time to try it. Btw, I do not recommend enabling this option if reading from a NFS server or from mechanical drives. IO reads for an input file are normally sequential with only one worker reading at a time.

MCE::Loop::init {
   max_workers => 4, parallel_io => 1, use_slurpio => 1;
};

$ time ./mce_loop_script.pl
nose cuke karl
nose cuke karl
nose cuke karl
nose cuke karl
nose cuke karl
nose cuke karl
nose cuke karl
nose cuke karl
nose cuke karl
nose cuke karl
Took 23.541 seconds

real    0m23.670s
user    0m51.046s
sys     0m 7.150s
[download]

That chunks at 0.85 GB per second and not able to go any faster.