• graphics card
• size of the terminal
• state of the window - (partially/fully) obscured? iconified?
• color/monochrome xterm?
• font, font size

it's the amount of scrollback that has most impact on performance.

• Having a 83x68 xterm, fully visible, 5000 lines scrollback, the code needs 74 seconds to run.
• Firing up the code and immediately iconifying the window reduces the time to 41 seconds.
• Increase the scrollback to 1_000_000 and (besides consuming an insane amount of memory) xterm behaves like an old telex (I didn't wait for it to finish :-).
• Reducing the scrollback to 0 results in 8 seconds execution time.

--shmem

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}