Speed doesn't kill deer, accuracy does. Your arrow weight is fine for 65 or 70 lbs, so that isn't an issue, no need to increase it unless you think a heavier arrow will shoot better.
Can you draw and accurately shoot at 70 lbs? Can you draw and accurately shoot at 70 lbs in 20 degrees weather after sitting in a stand for 4 hours?
I can draw 70 lbs, but my bow is 62 lbs.