I have never thrown Motiv equipment so I can't really compare, but there is a noticable difference between the Taboo and the 718A However, if you would really like to use it for lower oil levels I would go with the 718A with certain caveats. First and foremost, the ball is extremely angular on medium conditions, so I would suggest drilling it with a weaker layout. Second, the balls finishing process stops at 2000 and then polish is thrown on...Personally, I would suggest knocking off the polish, running the ball through the progression, but if you want to really use it on lighter volumes I would finish the ball 2000 - 4000 - 4000 and then put on some polish. It should tame the ball down enough to allow you to still use it on medium conditions and the lighter conditions you want to use it on.
However, if you want a true light oil ball and you like track I'd go out and get a 505A while they are still available as I am not sure when they are scheduled to be discontinued.