I tried with the cold boot too but it doesn't measure the impact too. I tried also by disable the program and a proper shutdown and then again enable the program and did a cold boot again but nothing changed. SO there is no way to manually(according to me, if someone has idea he is most welcome) measure the startup impat.
So I recommend to use third party apps like Soluto which can measure the startup time and also show the solution to make it fast. Or you can use Argus Boot Accelerator for startup items.
Another tool that can measure the startup time is BootRacer, which is free for non-commercial use. The latest version of BootRacer adds support for Windows 8. Now its also available in Windows store.