I don't think Guerrero is as good as N'dam and despite the 6 knockdowns I think he's got a better chin than Guerrero as well. He may well give Quillin the runaround for a few rounds but Quillin should get to him eventually unless as you say his weight problems screw him up. Although didn't Guerrrero struggle to make weight as well?
Jury is still out in my honest opinion, clearly has a bit of potential and is very gifted physically. Im not sure he can push much further forward, if a reasonably gifted fighter comes along and can take the power or avoid it altogether does Quillin have much to fall back upon, time will tell.