I have a stock tank 22inch with a 3 core 5/8 tube rad, with clutch fan and shroud and my IMM built 408 pushing close to 600HP, and it stays under 180 with these cooler temps, and have never seen it go above 200.
Again, the temps don't seem low enough for what you're doing, and the current temps in Phoenix. What other specs on the motor can you share. I would expect it to be able to maintain well under 200. We're not even HOT yet here.
for evening temps right now, 220 seems hot. Does it slowly creep up and never cool down. Was this idling around or some RPM down the highway. Just some thoughts.