Scenario 1 goes to Silver mid diff at worst imo. He threw his fight with Gray when gray was using Ice Make Magic, and really only lost because of a steel ball. I don't see how Gray just getting DeS and being pretty much a complete novice with the magic doing much better than what he did, I mean Silver can't eat the ice but its still not going to really change how he'd go, especially if he fought seriously.
Scenario 2 is a bit tougher because Gray had half a year of doing work, training etc. with Juvia and then 6 months odd of infiltrating Avatar. So could he have gotten better with Ice DeS magic? Yes. Would he of reached the level of mastery with it that Silver had, knowing Silver spent numerous years to master it? Probably not. So Gray wouldn't be as efficient as Silver with the magic, and it'd probably come down to power in the end, and there's no way to currently gauge how strong Gray is without comparing him to someone like Erza, who is slightly above him, and then you have to consider Silver never went all out against Gray, let alone take it that seriously. So in saying that, I'd give it to either one high diff.
