How much does PvP node value decrease when you gain points?

Quebbster

OK, in Stay on Target I am currently shielded at 1180 points and waiting for health to replenis before another shield hop. I have 3 good targets lined up: four-star teams worth 75 and 70 points, and a two-star team worth 50 points. I assume the latter is someone who's done climbing.
Anyway, I was trying to come up with a good plan to reach 1300. Obviously I can get there by beating both four-star teams, but that will take precious time that will leave me vulnerable. The two-star team would obviously be a faster game, but the question is how much gaining points will decrease the other nodes. Anyone have a good rule of thumb?
I usually estimate the decrease is around 10% what you earned from the match, so if I win the 75 point game the other nodes decrease by 7-8 points. That would mean the 50 point node decreases to 42 points, leaving me just shy of 1300. On the other hand, if I do the 50 point node that might drop the 75 point node to 70 points, giving me 1300 points on the nose. Does that sound plausible or should I just go for the two four-star teams?