Using the PCA module as a 16 bit timer doesn't give you quite the accuracy required; much will depend upon the interrupt latency, which will likely depend upon the rest of the software. As a high-speed output part of this problem is worked around because the ouput is toggled before the interrupt is given. Nevertheless will it be required to reload timer values in the ISR. With a latency one has to take into consideration here, too, the full 16-bit range required can not be obtained. So : yes (Erik) the PCA module can be setup as a high-speed timer ouput and in that case it is a 16-bit timer, but no: it isn't a full 16-bit PWM. It may come close, but it still isn't.

When setup in 'true' PWM mode, you have full control but with a resolution of only 8 bits.