Radiator upgrade experiences?

Looking for input on changing from a three-core to a four-core radiator. I am familiar with all the other 'stuff'...fixed flex-blades/viscous drives/shrouds/fan depth etc. NOT asking for anything about that.

Has anyone experience with a three to four-core change and how it affected their cooling issue?

Maybe even input on horizontal vs: vertical flow radiators if someone had a good result with such a change.

I do run a tad hot in traffic and at highway speeds on hot days. It's not awful, but I could do without it just fine.

Thanks!