Actually, pokecheck yet has to implement their 6th gen support. Instacheck was used in order to reveal hidden values.Pokecheck is what people used to check their shiny values, but Nintendo released a patch that kinda made it not work anymore, so it's impossible to know your shiny value now unless someone comes up with an updated version of the Pokecheck that works with XY or something.
I don't think high/low numbers are relevant with shiny values.
How high or low the numbers are is not important. The Pokemon will only turn out shiny when the number matches the personal Shiny Value. That said, the number is best when it is matches your own, second best when it matches a SV of someone on the Shiny Hatcher Community Database (providing they are still alive and active in order to hatch the egg).