Got it. My logic started with a flat roof, rather than the other way...I figured at flat there is zero pushing out, but that is not really relevant and a whole other story.
By my calcs.....ties on the rafter/wall plane and 6/12 pitch is about 2,000 lbs (using your calc example) lets me double the load by spacing every other one and have load about like a 3/12 pitch.
In real life,the roof side is about 24,000 lbs at 20/20 loading, so that is 2,400 lbs per tie, skipping a rafter at 24 in spacing and 40 feet length.
Since the tension is outward, the assumption is there is not a lot (any) bending/twisting force on the tie, so it becomes a task of fastening them on the ends to resist that "pulling" force and enough dimension to keep from sagging in the middle. Sounds like 2x10 will be OK. This is all figured on SYP. Still working on getting the figures that compare for the species I will use. Currently the wood i am considering is about 30% stronger in bending/breaking than SYP...but that remains to be verified.