The johnson pump might not do too much bceause the stock system is restrictive... More pumping power but still pushing against a restrictive system. Maybe search back through Waldig's extensive posts on the heat exchanger studies and upgrades.

I eventually found my winner by keeping the stock pump but parallel'ing a second heat exchanger with the stock heat exchanger. Basically when the pump output hits the restriction limit of the stock exchanger it just spills over to the second exchanger and both exchanger outputs unite before reaching the intercooler above.