Nice topic, spent a lot of time myself on these \'cube generators\' and ive accomplished the following.
Dimensions - Blocks - e/sec - e per block
3x3x3 - 15 - 2051.6 - 136.8
5x5x5 - 64 - 4992.8 - 78.01
7x7x7 - 167 - 26,789.5 - 160.4
This tells us to stay well clear of 5x5x5, you could...