I've heard good things about Carvins, but I've never had the chance to play one personally. I don't know that the neck shape will be any thinner than a C. You might want to look at a Jackson too because that would seem to fit all your points. For sustain purposes to might want to eschew a Floyd and just get a hard tail. That said, I don't think my DK2M is lacking in sustain at all. The advantage of a Jackson, as opposed to a Carvin, is that you could try one in the store before buying. There are deals to be found too. I got my MIJ DK2M on closeout at Guitar Center for $299.