i think u should go the other way around. U may choose any ball to practice, but all ur practice may fail u, if ur match ball is different from the one which u practice with. Ideally try n figure out what is your match ball and then practice with that. it should help give you a better idea. But then there is not much need for you to keep changing balls to practice ur kicking. i think if u practice with a heavier ball, u will end up getting used to kicking the heavier ball to a fixed distance and then get better distance once you move to a lighter ball. So my take would be to either practice with what u have now if its the Match ball nothing like it. And if u really wanna buy a new ball. try buying the match ball, or the one which is heaviest. Match Ball for better feel and accuracy during your matches. But the heavier ball, if your looking at training yourself to get distance.(If you're a "Francois Steyn" fan)
Yu should be able to kick with any balls. Your not going to have a choice in a Match. So just practice with all balls. But Gilbert balls would be the best.
