if yer bow is cut to centershot, or fairly close, shaft spine will be far less of issue - perhaps no issue at all.
i mostly shoot those cheap beman ics bowhunter shafts. i have one shaft size, the 500, and my resulting 29" arrow works well out of all my longbows, from 43# to 55#. i pull the full length of the shaft and my woodsman heads touch the front edge of the riser as a sorta 'draw check'.
i tailor the arrow's weight by varying the front end weight. arrows range from 430 to 590 grains. they all fly just great - FOR ME. and therein lies the crux of the matter - all talk about what will or won't work for each of us, Particularly With Carbons, is just a starting point and each of us needs to put in the testing. your form plays a critical role in arrow flight, as well.
in your case, i'd probably wanna go with an ics bowhunter in 400 spine.