Agreed. Whitetail are not hard to penetrate, so long as you hit them in the right place. While I like pretty heavy arrows, I shoot at a lot of bigger animals. I'm committed to lighter weight bows now, and I like 9-10+ gpp out of the low 40s for deer and antelope. There are a lot of guys who do very well with 9 or less gpp.
That said, I encourage you to test to see if the heavier spine will work well with a bit heavier head. But, if they don't, accuracy and a razor sharp broadhead is more important than mass.