Mike,
This question gets right at the heart of a post I started this past weekend in response to Jason's (Lb-hntr) video on how he achieved UFOC by double inserting. If you're just interested in total arrow weight then conventional wisdom says when you simply start adding point weight you're eventually going to weaken spine to where you have to shorten that arrow or go to a stiffer spine. If you want to go heavier and increase FOC at the same time, then there is another path to get there and possibly use the current spine you have by making it stiffer with double inserts, but I don't want to drag your post "off in the bushes". You can watch the video for yourself and decide what's best for you.