PMFJI:
When the minimum no. of ranked rounds have been played bad rounds won't count to the average. This includes only the (minimum no.) best rounds of the active tier. Then, the effect of a score depends on the fact if and which higher score it may push out of the average. I doubt that any score above 63 will be in the mix when s.o. tiers up to Legend.
No reason at all to quit a round.
Also, don't think in -5 and whatnots but in absolute score. A -5 @RSG counts 65, @STA it's 67 - big difference for the average! Even more in 9 hole rounds, since the scores are doubled.