Which one flows better, factory 6 blade water pump or 8 blade

the thermostat regulates to a minimum coolant temp, unless it sticks.
The maximum is governed by the ability of the designed system to get rid of heat. Stopped, at idle, with the hood closed, is usually the hardest case.
Your fan is trying to create a low-pressure in the shroud. Higher pressure atmosphere is trying to oblige, but with the hood closed; the engine is loosing heat right thru it's mass, and the headers are cooking everything in sight,together those two are opposing atmosphere right at the shroud. And if the engine is simultaneously sucking that almost super-heated air, it is just feeding the fire. No fresh air is entering the underhood, because you have sealed the cowl and sealed the core-support. so the underhood air is like a runaway nuclear reactor.
So some of that hot under-hood air finds it's way into the shroud and voila , no low pressure. No low pressure PLUS the air there is now 300 to 400 degrees.
The rad depends on the atmosphere pushing it's way thru it. Atmospheric pressure is very low, compared to what a 7-blade hi-pitch direct drive fan can create in a tight-fitting shroud. But when the underhood pressure is greater than the pressure in front of the rad, it just can't do it...... at idle.
The proof is in the pudding; just open the hood and let the hot air out. Then increase the engine speed to restore the low pressure area in the shroud.
The tight-fitting shroud and hi-efficiency factory style fan are your number one warriors in the battle for cool air.
You have to stop thinking that the fan somehow sucks; it does not suck.
The fan just moves air. It flings air radially towards the tips. When the air leaves the tips, it is supposed to hit the shroud and redirect towards the rear. But if the shroud is too far away, or the pressure on the engine side is higher, then the air will be much more willing and eager to return to the just-created low-pressure area in front of the fan. The hi-pitch factory fans have the tips bent to the rear, in an effort to reduce the air from going back around the front. The tight-fitting shroud acts like a duct, slamming the door to wrong-way air.
After that, only the rad stands in the way of higher pressure atmosphere from dive-bombing the engine. But you gotta help it.Your fins have to be clean, bare, and straight..
By personal experience;
I have found the Chrysler hi-efficiency, all-steel, hi blade-angle, curved-tip, large diameter,direct-drive fan, to be the best candidate for the job; in a tight-fitting shroud,half-way into it. If the rest of your combo is set up right, it will be impossible to overheat your engine. Once you have proved your system works, then you can start taking short-cuts.
The first short-cut I took, was to get the same fan in a clutched version, and installed a thermostatic clutch on it. An early 2000s Ford Pick-up showed up in the shop one day, and I heard that clutch cycling, and I just had to have one of those. On lunch-break, I went straight over to the dealer and got me one.
With those two settled, and the hi-flo Milodon, the Hi-flo stat,the blocked bypass, 14* of idle-timing, and fresh cold air to the carb, My overheating days were over.
The second short-cut I took, was to underdrive my pulleys in a preemptive strike against the belt derailing at 7200 rpm. I have a 4 speed, so as soon as the car is moving, it is rarely under ~2000 rpm.
In my system the 195 stat sets the minimum temp closer to 205*, And the T-clutch sets the max to ~207*
This; with a factory 1973 26" 2-row, A/C ,Dart rad, in a 22" factory core-support window. And no header-wrap. Hood seals still in place. Hood all the way down, all around, no tricks.
My rad runs 30* cooler at the bottom than at the top; so 207/177 or thereabouts, at idle, with the hood open mind you, so I can shoot it with the IR gun.
At the time I set this up the 367engine was running a 292/292/108 DC cam, with OOTB Eddies at 11.3Scr and the same 14* of idle timing. Since then, that engine saw a 270/276/110 at 10.7Scr , and currently runs a 276/286/110 at 10.95Scr. The cooling system has been rock-steady since year 2001, with no other cooling system changes..
Happy HotRodding.