Rupture does not magically become better than eviscerate at any insight level. BG is a flat damage increase, if you are at shallow insight it's +10% to both rupture and eviscerate, at deep insight it's +30% damage to both rupture and eviscerate. You can ignore your insight level when applying rupture.
The only thing regarding rupture that you should never do is clip the last tick of a higher insight rupture with a lower one. THAT is a dps loss. It is ok and in fact a damage gain to clip the last tick of a lower insight rupture with a higher insight one, but don't go out of your way to do that.