Using .500 spine shafts on a 42# bow with more length and weight up front makes perfect sense to me if you want a heavier arrow. The more I tune carbon arrows for myself and others, the more I feel that it is a mistake to cut a carbon arrow shorter than 29”, regardless of draw length. Carbon arrows seem to become less forgiving as length is cut. While I prefer a 29” arrow for a 28” draw length, I find it much easier to tune a 30” carbon arrow than a 28” carbon arrow, again regardless of draw length.
Could try a .500 spine at 29.5 with 250 up front. I think the arrows you are shooting are perfect though.
Using .500 spine shafts on a 42# bow with more length and weight up front makes perfect sense to me if you want a heavier arrow.