I will never put ss on my gear after I did tests before novus. I had a set of gear that had a good amount of spell speed on it, and when removing the set to be naked basically, it was about a 100 point difference in ss. With about a 100 points difference in spell speed, the speed it increased my cures was exactly .08
That is atrociously low for 100 points.
Btw incase you didn't know, the exact cast time can be checked by looking at the actions and traits menu and it does update with stats, that's how I knew it was exactly .08

Though ss does make a bigger difference to blms. I don't know why, maybe it's because it's offensive magic? But for healers spells and buffs it's garbage