For core computing 8 you'll need to be able to basically max the 2.0 weapons. 9 is "possible" at the moment but is not actually realistically doable as there's just not quite enough compute power/speed in the game at the moment to achieve it in a reasonable amount of time.
the normal soft limit is +100%, the soft limit in the challenge is thugs +1000% or 10x. or at least I'm pretty sure it is. You can tell if you're at the soft limit or not by going to the stats and info screen and then looking at statistics and wave clears. It soft caps at 1000 wave clears, so if you have less than that it's a a ways to go yet to the soft cap