Here is a good tutorial on optimization without any installations: Optimize Windows 7
So in safe mode, the computer is worse off than normal? It starts up slower, but what about the the shut down time? Safe mode shouldn't load any peripherals except mouse and keyboard. Try unplugging things that you don't need (except mouse, keyboard, and monitor). Go into safemode without networking and see how long it takes to start up and shut down. This is only supposed to test to see if a potential problem exists with a drier or program, but if there is no difference, then perhaps the issue is more deep.
75 seconds is a really long time, but I wouldn't worry so much about that as it wasn't the problem to start with, was it? It was the shut down time. Check the BIOS. Are you overclocking? Test the BIOS in its default state to see if it helps at all, and you might even consider flashing it.