There is nothing such a base ammount of skill giving ability to open lockers.
Anyway, I think something more than 75% + lockpicks is good start. Anyway, to open all locks and have less fails I would prefer to get somehow fast to 100% skill and use lockpicks with 25% bonus. From now on, you should open almost every lock.
If you have spare skill points, put them in lockpicking anyway to get 125%, from now you should open almost every lock without lockpicks, and all locks in 90% cases with normal lockpicks.
125% gives you ability to craft extended lockpick set, it will give you 50% bonus. With this set of lockpicks and new base of 125% skill there will be no locker that can be safe from you. Anyway I dont think putting more points in lockpicks is good idea, only waste of skill points as for me. 125% is enough, no need to go to 150% hard cap.