I personally would base it on DVD performance since I think there are some belting performances on there, and some more average ones, but just so long as the DVD performance plays a key part in it I don't really mind how people vote *. I did think of doing double nominations (and consequently double eliminations) in order to avoid it dragging on for about 2 months, but I can imagine the admin for that would be horrible
* - For example, if someone likes two performances equally, but chooses to save one song as they prefer it, that's fine; but if they just vote to save their favourite song regardless of how it is performed then I'm not too keen on that.