Justin,
Do a google search on the AMO spine deflection chart.
Once you have that,print it out an tack it to the wall beside your PC.
It lists the correct spine deflection for everything from 20lb too 95lb.
Once you've done that,go to the web site of your chosen arrow manufacturer and you will see they list the deflection of each size shaft they make.
From there you can make an informed decission on over all length and point wheight.
The AMO chart will give you a solid base to work from.
If you can't find the chart,let me know and I'd copy it and post it here.
Cheers.