I ordered 2 of the 8x4x2 and got exactly what i needed. A 6x3x2, lol.
The 8x4 would have been awesome but  
I’m happy with these big boys and they are deep and made pretty well. We might reenforce them…. We’ll see. The will look great with the six in total that we purchased. I’m happy that we don’t have to deal with rotting wood and these should last for years. I think they’ll look really great when they rust.