Go read my post in the other thread, it will illuminate for you why there is most certainly a line particularly with the caster role. Potential buffs to RDM very well can and most likely WILL invalidate any buffs to BLM because if the single target damage of RDM creeps up closer to BLM even with buffs, it will still be stronger to just take RDM and BLM will be even further in the outhouse.