I wasn't trying to say 8/0 was necessary, just that you couldn't realistically increase the gauge to compensate for a relatively large change in length. Also, you couldn't make such a modification expecting no adverse effects whatsoever. As I said, the performance impact of separating the motor and controller is much harder to calculate than just the simple resistance involved. The resistance may not be a significant factor, but it would be similar to running your motor/controller config as they are now off a 5 gauge wire (or 3 10 guages) instead of the 2/0, which isn't something I would want to do.
I haven't seen any conversions (not to say they aren't out there) that have significant motor/controller separation, so I don't know if there's any real-world data out there.
The simple thing would be to test it out with a quick mounting and a test run to see if your performance or the wire temps are affected.