Full exhausts to open headers gain

I don’t recall the details for pretty much all the combos where I’ve seen that tested....... but I do remember one.

SBC 406”, 13:1, roller cam, single plane, too small headers for this motor(1-3/4), 5000 stall, glide, 4.30’s w-28” slicks, in a 65 Nova.
Mid-10 second car.
The exhaust system was 3” pipe to 3” flowmasters, with the pipes exiting in front of the rear tires.
Removing the exhaust and installing collector extensions was worth almost .3 and over 2mph.

Most of the loss with the exhaust I attributed to the flowmasters.

In your case, it’s really just a matter of...... try it and see...... then iiwii.
No point in overthinking it.