I think the P300 has plenty of power. Comparing the 300hp of the defender vs the 300hp of my LR3 is very different. The 8 speed transmission I think makes the difference and the turbo spools up early. It feels much quicker than than LR3. On the Mojave Road, the 4 cylinder sips gas compared to the V8 as you aren't on the throttle much. Of course the P400 has more hp and u can feel it, but I dont need it and wanted the 18 inch rims. Also didn't want the extra burden of LR electronics to go wrong in the field. Mine is as basic as can be with no sunroof, sliding seats but still the offroad packages.
Ironically, talking to the guy who runs the Land Rover Experience in Carmel, they had a P400 with electric seats. The electric seats stopped working one day and dealer couldn't figure out why so the defender was sent back and never returned...