From what I currently see:
4R70W can be built just as strong as a C4. Also OD helps fuel mileage and keeps RPMs on the highway down.
If your car is only used occasionally and on the weekend, then overdrive may not matter to you.
4R70W would cost alot more though (expensive). Also it's heavier and soaks up more HP than C4.
Powerglide is the lightest and eats up less horsepower. Only has 2 speeds but the 2nd gear ratio is 1:1 just like a C4 in 3rd gear.
On the highway the RPM of a Powerglide is the same as a C4.
The disadvantage of the Powerglide on the street is that 1st gear is very tall and you need good low end torque to get it moving (maybe your 408 makes good torque down low?)
Powerglides were production transmissions and were used on the street however.
With 3.27 gears and 26" tires at 60mph would be about 2600 RPM
The advantage of the Powerglide on the track is that the tall first gear makes launches more manageable when leaving off the line with twin turbo boost or 500 hp nitrous like you intend.
Plus the powerglide is cheap to build strong. Also you only shift once!
Each has it's pros and cons. You have to decide what is important to you.
You really need to talk to someone who has one. Try the site I mentioned.