Your methodology is flawed.
The Cube Orange+ and Pixhawk 6C are, for all intents and purposes, equivalent hardware. The Cube’s heated and damped IMUs are largely irrelevant for the slow-ish inner control loop utilized by and lack of 6DOF stabilization required by Rover firmware.
The only difference between SimpleRTK2B performance and any other Zed-F9P based system is antenna choice, which you have not specified in the case of the SimpleRTK2B. Practically speaking, though, you could expect identical performance.
Additionally, you’d be hard pressed to note a real, practical difference between UM982 performance and Zed-F9P performance in a Rover use case.
Essentially, given the options presented, choose the price point and form factor that most appeals to you. If you feel you have the skillset to eek every last drop of performance from your system, the Cube Orange+ and pair of SimpleRTK2Bs coupled with survey grade antennas would be VERY slightly preferable.
And why not just continue the conversation you’ve already started here?