My Halos are just fine over potholes.
A "heavier" spring rate will indeed stiffen ride, if you are just talking about a higher spring rate. Something like a Deaver spring has a more progressive rate than the stock spring by having thinner, but much number of leaves. So as the spring compresses, more springs are "engaged". (this is an oversimplification as all springs are technically bending since the springs are touching, with the exception of an overload spring, but you get the point).
This is one of the reasons I'm still hesitant about the RAS system, it's combining the stock springs with a progressive spring rate with the more linear coil spring. It's a bit of a Frankenstein setup, I'd rather just spend the money on a proper spring pack.