Theres *probally* more to it then just him testing his limits but Kishi just hasn't put it in yet. But if he doesn't then it is dull imo.But I really don't get why test it on your clan... Kishi should've added some more story into this. All we got was that Itachi wanted to test his limits, but that's a bit dull to me. Unless I missed some stuff.
Anyways id say Kakashi is cooler cause Itachi pisses me off and wears women clothes and paints his nails purple..