Not driven the L405 V6 petrol, but I did drive the same engine in a Jaguar XF. Fast. Quiet. I noticed the transmission (8 sp auto) was very busy to keep the engine at its sweet spot. It worked great in the XF but I really wondered about a heavier vehicle. My RR seems to just pick a gear going uphill and then just plots on using torque until I get to the top. The V6 didn’t seem to have that endless torque. You’ll need to try it for yourself.