This morning was my first chance with the APM150 to view the gas giants with good seeing and also be high enough to clear the trees completely.
I had some amazing views of Saturn and a transit of Jupiter with the APM150 using the 12.5 Doctor's and 12.5 APM's.
Io's shadow cast a distinct black dot that is surprisingly easy to see at 66x. I could occasionally make out the tiny white dot of Io itself back from the shadow.
It looked at first to be one of the small white ovals in the color band, but it slowly changed position with the shadow. The bands across the planet surface were sharp and distinct enough that it appeared as though I was using a much higher power.
The perceived size of the planets at this power is really impressive using both eyes. Without measuring exactly it is hard to guess, but it seems to require more power in a mono view to equal the image size of the bino view.
There is also a clear improvement in brightness and resolution compared to the APM120, and a huge improvement over the APM100 for planet viewing.
I noticed the same size effect when comparing the 12" SCT and APM150 on M13. The 150 was at 103x while the 12" required 194x to provide a comparable overall view. This brings the exit pupil closer in size as well, which equalizes the background darkness.
The 12" resolved more stars at either power, but the fullness of the cluster appeared larger in the 150 when the power was equal.
Of course, these observations are only my perception of image scale and brightness, not precise measurements with these particular instruments.