I have not hiked the PCT, but have read the journals. There are many places to switch out gear so do not think one-size-fits the entire route. I would think you would be better off with the best match of gear for the conditions for specific sections. A good read would be both 2012 and 2011 PCT journals - conditions were very different for each year.

I have used a bivy a lot in the Sierra at high altitudes (alpine climging) and it works. But it may be overkill for the PCT where you will be camping lower and have timber most of the time.

You need to think of a "sleeping system" rather than just a tent. Pad, bag, shelter and perhaps groundcloth all work together to meet your needs regarding warmth at given temperature, chance of rain, bugs and weight carried. You do not need a groundcloth with a bivy, but perhaps would need it with a short pad and poncho.

Listen to BrianLe. He has more experience than all of us put together!