The D300 will put more pixels (12.3 MP) than the D4 (6.8) on the subject when using the same focal length.
Taking the pixel density of the sensors into account, the D300 will get the same number of pixels on a subject using a focal length that is 0.773 times the focal length on the D4. For your lenses this means that above 387mm with your 150-500 on your D300 you will get more pixels on the subject than using 500mm with the D4.
The quality of the image is determined by more than just pixel count. The AF of the D4 is much better than the D300, so is the high ISO noise and image dynamic range. Also maximum frame rate favors the D4. All these could be important for wildlife. Pixels on the subject favors the D300, other factors favor the D4.
Personally I'd take both cameras. I'd never go to a such a remote and likely one time destination without a backup camera.
Gary in SE Michigan, USA. Nikonians membership - My most important photographic investment, after the camera. D4, D810, D300 (720nm IR conversion), D90, F6, FM3a (black), FM2n (chrome) YashicaMat 124, Graflex Speed Graphic 4x5 My Nikonians Gallery & Our Chapter Gallery