I would imagine it would be a bit like trying to loop a Phantom in cold power. Start with as much speed as you like, it's so heavy and draggy (especially when pulling g up into the vertical) that it's going to slow down VERY fast. The top of the "loop" would most likely become a nasty slow speed tumbling recovery.
She was built to be beautifully stable and fast at low level, not an aerobatic display jet. Buc aeros - an undignified dance for a very powerful and magnificent war fighter.