The original magic based GL, assume the ring isn't vulnerable to direct magnetic attack (since i've no idea if it's even a metal that's reasonable) what are the odds here - can Magneto be a serious threat to such a powerful opponent?
all the GL rings, including Alans, have the ability to manipulate EM as well. That said, there's a REASON Magneto is master of Magnetism, so, while in theory any top end GL can do what Magneto can, they don't posess the skill to do so.
That said, the GL powerset at its fullest is even more versatile than Magneto, and every bit as powerful, HOWEVER, Magneto is about the BEST at using what he has, so IMO this is a dead even fight that could go either way. They're true peers.