Need to spec up a drive shaft - Not sure how strong it needs to be?

I really don;t think you need the billet or the solid joints. I prefer to be able to grease them occasionally and your car should not leave anywhere near that hard. Most U joints break from driveline alignment issues than just overpowering. There's some really strong big block, heavy, stick cars that exceed that power level that are running stock 1350-type joints. Aside from the balance issue, a stock type shaft would be fine for that performance level. It's not a bracket car with skicks and a brake. It's a street car.