1.5 vs 1.6 rockers

How about the "stress" on the other side of the lobes, you know, when the spring/rocker force is HELPING rotate the cam?

By the time you have gotten to lobes and spring big enough to matter you should have roller lifter already.

I was being sarcastic. Just pointing out that the increase in "stress" to open the valves will be partially offset by the force of the spring/rocker on the closing side.