i remember myself surprised from how fast boot speed the RB1100AHx2 has (maybe 5-10 second). was expecting this boot speed from hex s or ccr1009 but they are not even closer. why?
my rb2011 boots at 30sec. boot speed for me starts when i press reboot at winbox until i hear 2 beeps.

It can be affected by the settings of /system routerboard settings.
E.g. the setting for boot device "try ethernet once then nand" which is preferable when you want to be able to do netinstall
without jumping through hoops with reset button, of course costs extra boot time.

tried your suggestion on hex s that has very powerful cpu and it is not even close to rb1100ahx2 boot speed. truth is hex s boots like rb2011 speed.
so what makes rb1100ahx2 boot speed so special?

Generally it can be said that boot time is not only dependent on CPU power but also on "constant" delays in the boot process.
The bootdevice setting I mentioned is one of them.
On devices with a serial port there can be an additional delay while the bootloader waits to see if the operator at the serial console hits a key to enter debug options.
Devices with little flash and a lot of RAM can be de-compressing the firmware from flash to RAM on bootup, also costs time.
Etc etc.