i'm afraid  have no other measured times than the above mentioned. i was so busy completing the project that i wasn't able to do tests.

from what i have experienced i believe the tiling of the render is the most optimizable part. but also the network speed will determine how fast the overhead is handled.

before the actual rendering of a tile/frame starts the geometry and textures are distributed to all rendercows and after the rendering is finished the calculated image is collected at the host. this is what i call the overhead and what "get's in the way" of the pure rendering time.

also i have no experience with animations. i dont know if the overhead time is spent another way (does it send all textures at the beginning or does it start sending texture only if they come into camera vue?)

basically i would expect that the longer the render time is the more benefit you would get from more pc's. if single tiles or frames are calculated "too" fast then the overhead might turn out counterproductive.

as soon as i have more comparisons i will post them here ...

good luck
chris