Sorry for the extremely late reply, as far as i can tell from 262 videos, and data, the Riedel could spin upto 10,000 rpm, maybe much higher upto around 15,000 rpm - they were reduction geared down to the starter dog gear, before the even more reduced gearing on to the engines starter drive ring - Reidel was ready to be switched off on the 262 Jumo's when the engine was able to run itself was at over 800 turbine rpms once the engine was igniting its fuel, and I believe once 900 (turbine)rpms was reached the Reidel was shutdown.
Reidel's didnt use fancy porting or Kaaden/expansion pipes, nor are details to their cc found often - I think 350 to 450cc might be in the ballpark.