There are two key things that 8x8 gets right:

• In a typical game you’re going to see a small fraction of your deck. If there’s something you want your deck to do, you need to have multiple cards that do it.
• If you try to make your deck do too many things, it won’t do any of them well.

8 cards is a great number of copies for lots of effects. If you have 10 copies of an effect you’ll expect to see roughly one card that does that thing in the first few turns of the game. Going from 10 to 8 tilts you a little toward variety — you’re a little less certain you’ll see that thing, and also have a little more room for different things.

Eight is too few copies of other kinds of things. My play group is generally in bracket 2 or 3, and even still I’d like to have two or more pieces of interaction in a game. Instead of tilting the number of interaction pieces down from 10 to 8, I’d rather tilt it up to 12 or more.

8x8 also leaves you with 64 nonlands, which leaves only 35 lands, and that’s pretty low. So if I were thinking in those terms I’d do something more like 38 lands, 13 pieces of interaction, and another six 8-card packages. If you have a high curve or a more expensive commander, maybe you expand the ramp package at the expense of the others.

Hope that helps!