They both have the potential to grow equally, and 5 different san pedro cuttings will grow 5 different ways, so it's hard to say.  i've regularly bought 2 identical cacti from the same distributor and had completely different grow rates:  one starts shooting off limbs right away and grows an inch or more a month, and the other doesn't show any growth for a year (eventually growing, though slowly).

you just have to pray for the best.  growing indoors will slow it down, and growing it in a pot will slow it down, but don't let that discourage you, it's still rewarding!