WOL has nothing to do with Standby or Hibernation.
It is a method to switch On the computer by using LAN connection,
What you would like is not a matter of software or OS,
As far as Normal PCs go, when it is witched On (whether it is done by the switch or WOL) it has to go through the post-boot sequence. I do not know of a regular computer that post-boot in 5 sec. It is more like 15-20 sec. (or more)
Once it is finished with the post-boot process it loads the OS.
Windows loads the fastest if it was hibernated.
You probably can find specialty computers that might do the hardware boot faster but No matter what the combo of boot and load OS will be more then 5 -10 sec.
The best you can do it build a File server using a mATX Mobo (810 or 815 chipset) with P-III class CPU stripped from all peripherals but the minimum necessary (can use KVM) to keep Files and leave it on in standby mode.
:sun: