Since your temp is 190 on the highway you get enough air while driving. I would shroud only the bottom and the sides to let fresh air circulate over the valve covers. Loads of cooling happens via the motor surface. That will also reduce under-hood temperature.
Check your temperature at 35 mph, which should remain at 190. Then you know you get enough air while in motion. Disconnect the fan.
Under 35 mph (every car is different) your fan takes care of the cooling. Basically you must be able to let the car idle endlessly and the fans do their work. At idle, since your motor is producing very little hp and heat, almost any radiator should be able to cool your car.
The real test comes in like this:
WOT on the highway (4.500 rpm and up) for a few minutes, leave the highway and end up at a red light and have to wait for three phases to make it over. Now your radiator and fans have to show what they can. This can be nerve wrecking.
Is your timing correct? Especially at idle and part throttle.
Lastly, IF you can go WOT on the highway and see a slow climb in water temp, this may actually be your
oil heating up the water. Then you need an
oil cooler.
And: While you have an indication about boiling, because your cap lets coolant out, verify your temperature gage reading! Wouldn't be the first one which is incorrect.