you will have some carbon or oil build up but not much, I would think rich should run cooler.
I like the idea of putting the stock rad back in and trying it, because high speed use, over heating tells me the rad isn't doing it's job correctly, I've seen some new rads that in the welding prosese the tubes partialy colapse and will not cool good. but the coolant still looks like it's flowing good.
I had this happen on my race car with a very good rad builder,they exchanged it problem solved for me.