This is correct. Running high voltage involves two primary considerations - motor kv AND available gearing. If you can gear 25:1 then there're only two things that might stop you from running a 2500 Kv motor on 8S - iron losses and motor quality. On a setup like that the motor will be spinning at 75k RPM at full tap. The motor needs to have high quality bearings capable of running at that speed, and the motor itself needs to be made of large/strong enough quality parts so that it doesn't break itself. As far as iron losses go, brushless motors generally need to spin below 250k RPM per pole. For a 2 pole motor this means 120k RPM. A 4 pole 60k RPM. An 8 pole 30k RPM, etc. This is why Neu 1500 motors are rated to max 60k RPM (4 pole), and 1900 motors to 30k RPM (8 pole).

The sweet spot for a motor is just below its peak RPM. This is where you will get the most torque and power out of it before heat becomes an issue. This is why I want to run a Neu 1912 at 30k RPM in my 1/8 buggy - optimal motor RPM and gearing is (fairly) easily available. I also think a motor that can run optimally at a lower RPM will result in less energy wasted in the gearing.

The problem I see with BP's setup is that he wants to run HV in a small car. This means he'll need to find a motor physically small enough with a Kv low enough for the gearing available. If you can find a motor with the right specs you will have one kick ass little car. :)