up to stick shaker, which might be very much lower initially and which incidentally gives the actual best performance
The stick shaker gives you a predfined margin to stall, but that only accidentially would mean it is the speed of steepest climb. You may already fly slower than the best climb performance speed if you pull up to the stick shaker.
However, If you do not have time to figure out the best speed, pulling up to the stick shaker is not totally off.
The speed of steepest climb is related to engine power, the stall speed is not. So that difference varies with OAT and wind. A clever modern PFD should be able to display it accurately...