I'm in no way a bow professional but Am I missing something??? How do you get the 200 is stiffer than the 300???
http://store.fastcommerce.com/thebow...2f55ca7-c.html
If anything they are over-stiff not under and in which case would not cause them to break under the stress of the bow string.
I'm running an X-Force GX with the same arrows set at 65lb draw with a total arrow weight of 390 Grains and I've never seen that problem.
I'm going to say the fletch job is the culprit, Or what ever chemical you used to clean them up before the fletch job took place.