just think of it this way, normal bricks are made up of rectangular prisms
the more there are, the more faces there are to be rendered, right?
if you have little cube studs on top, not even round, that adds 5 extra faces per stud on a brick
a 1*1 would have 11 faces instead of 6, a 64*64 would have 20486 faces instead of 6
overall the best case is you'll only be able to render half as many bricks before you start the lag
worst case is.. 1/20480th?
also, there's a brick texture that somebody made to look like lego studs
