For fun and laziness, I've got 20 entries in my GRUB2 menu. To get to the bottom one quickly, I tap down-arrow a couple of times during the GRUB loading screen. I can press the key 15 times (+/- 1, don't remember) -- the next press, GRUB beeps and the menu choice isn't affected.
Why would someone put the limit at 2^4 on a 64-bit processor? Is it even a GRUB problem, or is it caused by keyboard queuing?