I'd say it depends on how much distance between the two but current hulk seems much faster than I recall him being before so honestly I'm not sure. A empty city of metal is a mighty weapon be it lethal or just an avenue of distraction so magneto can possibly do something more complicated with his powers.
Would mags be able to BFR this hulk? Wrap him in a ungodly amount of city scape and launch him straight up into space.