I knew this would come up and I have been trying to decide how to word it. If you have large steppers this will/can help squeeze more power out of them. Do you need more power?
The kit I sell seems to be fine on the power side of things so I undervolt the steppers because the X and Y have enough power and then active cooling of the ramps is not needed. I need to tune the z axis, I ship it at about .46V but I think I need to start turning them up as people seem to be demanding more speed.
As is the drv8825 drivers with a tiny heatsink usually work at .7V just fine. If you put a small fan on them you can turn them up to a tiny bit over 1V without over heating.
That stacking way will make pot tuning harder to deal with. There is a $3 board on a few of the electronics sites that is a better option, it lays the drivers side by side, no soldering required, and I think you can use an external power supply, win win. If you do start to crank up the power watch the stepper temps they will quickly get hot enough to soften the PLA mounts. I prefer not to run my steppers much past “warm to the touch”