You only need 50/50 if you live in Alaska...I've run 70/30 for 30 years with zero issues. Get a $5 test kit and measure the specific gravity. Adjust your mix for the minimum winter temp (I use -10F here in Indiana). Any more coolant than that is just reducing the capacity of the liquid to transfer heat. The best cooling you can get is 100% water. But, that offers zero freeze protection...zero boil protection...and zero lubrication for the water pump. So you do need some glycol in the mix but, 50/50 is a "worst case" ratio that auto makers simply throw in to cars to cover their a$$es. In most cases, its overkill. A 30% ratio is very common in industrial cooling applications, and that works for me.
Also...it doesn't matter how much improvement in cooling capacity a new radiator gives you. The thermostat is what controls the engine temperature. You can hook your motor up to the Pentagon's (the world's largest office building) cooling towers...and it will still operate at the same temp it does now. Unless your t-stat is missing or its stuck wide open...radiator capacity should not come into play. There should be plenty of headroom (extra capacity) designed into the system, as long as its clean inside. But remember...this is GM we're talking about here...so all bets are off.
I do know of several Alpha owners that seem to struggle with engine temps, and I assume these are running at or past the capacity of the radiator to cool at full-flow. These guys will periodically have to "give their Alpha's a rest", which seems to work. For those trucks...I could see the extra capacity might be needed. Regardless...the thermostat controls the flow, and the temperature. I personally feel that anything short of a true mechanical temperature gauge (full-sweep dial and capillary tube) is in-adequate for getting accurate temp readings. This includes ANY gauge with a sending unit...any computer readout...and most definitely, the useless Hot-to-Cold gauge that GM gives us on the H3 dashboard.
In most late-model cars that have cooling issues...its air in the system. The sending unit is most-likely "air-bound", and its reading the steam head rather than the liquid temperature. The sending unit only works if its submerged in liquid. Pretty much all late-model manufacturers now require a vacuum purge system to drain & fill the cooling system. The days of "top off the radiator" are gone, and those rules don't apply to modern vehicles. The reason? The radiator fill cap is rarely the high-point of the system like it was before the 80s.
Before 1980...all cars were basically "boxes". They were designed so the radiator cap was the highest point of the system...and they were essentially "self-purging". But, as cars got more aerodynamic and pointy in the nose, and interiors became more modern with heater cores in unusual locations...we can no longer assume the cooling system will purge itself. Even when you fill the radiator to the top...there is often a loop that is at a higher elevation than the radiator cap. This causes a giant bubble to be trapped (usually in the heater hose to/from loop). This bubble is not static. It moves around and migrates within the cooling system...often under acceleration & braking. When the bubble hits the water pump...flow stops. When it hits the sending unit...you get a false reading. So its super-important to purge the system with a vacuum pump to get all the air out. If you notice your heater blowing cold air in the winter...take off real fast from a stop, and if you feel a burst of hot air come out, and then it suddenly goes back to cold?...then you have air in the system. This same problem can play hell with cooling issues in the summer.
