General

Both usually add 0-3

Cogs are 0-5 while Icogs are 0-7 and Miraculous are 0-10

COGs add from 0-5. ICOGs I'm actually not sure about. I've heard 0-6, 0-7, and 0-10. Personal experience from using dozens of ICOGs tells me it's probably 0-6. I'm also fairly certain that ICOGs are rigged so that getting 0-3 is much more likely than 4-6.

Regular CoGs can add up to +5 of a stat.

Most I've seen an iCoG give is +7.

I've gotten +7 from an incredible chaos scroll before, not sure if its the max though.

Chaos of goodness can add 0-5 atk.
Incredible chaos of goodness can add 0-10 atk.
It's not random. chances to obtain more than 5 is real low.