Cost aside - 700 rpm drop is not worthless. The 518 is better from that standpoint, but what option do you have if you don't want to hack up your car? Keisler GM adaptation? Better first ratio and as good or better O/D ratio.
IMO it is worthless when you consider a comparable or lesser cost option like a 500/518 or chevy 700r4 will deliver a much superior overdrive ratio.
