in reply to cat vs. file handle speed?

Think about the overhead involved. Here is my brief analysis:
open(INFILE,"cat textfile |") while(<INFILE>) {...}
This opens a type of file handle commonly known as a pipe. It spawns an additional process, complete with a duplicate set of environment variables and memory management requirements. The OS must now swap memory back and forth between Perl and cat.
open(INFILE,"textfile") while(<INFILE>) {...}
Perl opens a file handle directly to the file. No other processes are started.
system("cat textfile |")
Perl invokes the shell which invokes cat and another instance of Perl! Plus the shell still has to open a file handle for the output of cat / the input to

Result: All three methods require a filehandle (aka a fileno, or a file descriptor) and two of the methods have the additional overhead of multiple processes. Use the second method and avoid all that.