I don't do savage or ultimate but like using BLM in other contents. I liked stacking spell speed regardless of optimization because it feels better with lower recast time, but sometimes it will be slower when I level or item level synced. Because of this, I think the recast time should be fixed to your unsynced stat. The only thing I can think why it's bad is it will be overpowered in something like ultimate, but i'm not sure since I never did it.