What Leo said its all rotation based. Its same for (healers) spellspeed I know by default when to apply my adlo/stoneskin as i learned the rotation. All I can say I actually noticed a lil more time i have for dpsing as my spellspeed increased a lil from first time T9 (i102 iirc) to now (OP i116/117). But basically skillspeed/spellspeed are for most classes rather useless except to push a lil more when you use your burst cds (war esp here on berserk).