I've thru-hiked the entire PCT twice, both times with a SAK Classic that was adequate, if not overkill. The next time I thru-hike the PCT I will bring a small-medium fixed blade, Mini-northstar size, just for fun (and because I love knives.)
A normal-frame SAK and/or a moderate fixed blade will do you just fine. Those who suggested a folding saw give good advice -- these really provide a lot of cutting power for a relatively lightweight package. (I had plenty of fires on my PCT hikes and never found myself needing a saw.)
I agree that a machete is not necessary at all, but if your hike will include the infamous
Section O, you will find yourself wishing you had one!

Of course, if you did have one, you would probably tire of chopping after a mile or so and just push thru the overgrown trail like everyone else.
In a month, you could cover a good section of the PCT -- which part are you doing?
Whatever sections you choose, you will have access to at least a Post Office or two, so you could always mail home any extra gear that you do not want to carry any more -- in fact, I highly recommend this classic long-distance hiking rite of passage. It is a humbling and valuable exercise in flexibility and pragmatism.
Have a great time, and please remember to take and post lots of pics, especially knives-in-backcountry-action pics.

:thumbup: