[Zeke]

You should run the 4 th wire. That's code. The technical side of this is the white neutral sends current to the neutral buss as you likely have 120v controls and fans in the new oven. Not always but the schematic on the oven will tell you.

AFA the equipment ground, has to be green or bare, that goes to the grounding buss in the panel. Grounding is usually referred nowadays as the equipment ground while bonding is another thing. One thing for sure is that conduit of any nature is not considered a ground path oi most cases. However, if the conduit is bonded at each junction, it can serve as an EG. Rigid conduit schedule 40> is considered the min requirement, not some spiral flex.