It's not that "moving stacks is OP", there have always been ways of doing it in mods, but there has always been a cost, even if that cost is fairly low. Engines more powerful than the redstone one have always been able to move stacks like the RE-Cell can, Tier 2 RedPower machines could do it, and in the new BC you can use a level 7 Autarchic Gate to move stacks. There are no hard and fast rules about cost and balance, but it is generally regarded as rude just to implement similar functionality at a drastically reduced cost. You get accused of undercutting to gain market share. Right now we have a baseline cost for a device that can move single items fairly slowly, the vanilla Hopper. So if a mod block can move items more quickly, it should probably have a higher cost in some way. A Golden Hopper maybe?If ANYONE thinks moving stacks is OP, wake up and put a redstone energy cell against a wooden pipe and see what happens.