Depends for what Char and what ability

For Barbs if using Berserker Axe (base speed 0) you'd need 36%, by using Phase Blade (base speed -30, much faster) you'd need 6% so any ias roll is fine.

For Zeal without Fanaticism (Tesladin for example) you'd need 32% on Grief if bringing 40% more ias on gear (72% total needed so 20% from gloves, 20% highlords + Grief usually), if using Fanaticism you will cap ias even with a 30% roll.

If you get 30% when you'd need 32% and don't wanna reroll, for pvm you could add an ias jewel into Gface if using that or just add a belt with 10% ias, or Death's Disguise set 2 piece bonus belt + gloves gives 30% attack speed instead of 20% you'd get from Laying of Hands, some life leech, 15% all res and cannot be frozen