Some great points! Agree 100% that OEM is the best solution for street use. However, if you are putting in anything over the Raceshop Rollbar, I would not drive it on the street as you have the potential to bang your head on the cage which can cause MAJOR damage to your nogin. I am sure though you were referring to track use only. As you hinted at as well, you should always use a rollbar/cage, seat, and harness together. At that point, I'd feel comfortable taking out my stock steering wheel and putting in an aftermarket one(given it is being used for the track).
The Raceshop/M2 "Rollbar" is prob. more than you are thinking it is, maybe not. Here are a couple of pictures of the one in my silver car for reference. They also make door bar's on some models. I ran this season with the M2/Raceshop roll bar, Recaro RZ seats, and G Force 6 point camlock harnesses and felt safe in the car. But who knows for sure, it was never put to the test.
IMO, take it for what it's worth, I'd feel just as comfortable if not more comfortable running the M2 Raceshop roll bar, a fixed seat(whether it's your OEM Recaro's or the SPG's), and a harness on the street.
As far as harness's go Phil, I'd get a 6 point. Most 4 points won't pass tech inspections at the track and the 5 points can get real uncomfortable for us guys
