Are you going at a pretty typical time of year? I.e., late April start perhaps or thereabouts?

Is it important to you that the gear last longer than a single thru-hike? I have no experience with zpacks packs or tents; I have perhaps 3500 miles on my ULA Circuit, however, and have carried a different Tarptent for quite a number of miles too. ULA packs are pretty durable for the weight.

Are you confident that you can pack a bear canister and all your other gear through the Sierras in either pack? Assuming your overall gear bulks out proportional to other choices, the Circuit would handle it fine (and did so for my JMT hike this past September); maybe the zpacks model will too (again, I don't know).

Just in general, 3 pounds makes a difference that you can feel, particularly if your overall base weight is in the range you're talking about. You can also feel that difference by carefully planning your resupply stops to not carry more food than you have to.

If you think that the lighter zpacks options will survive and thrive to be used for a lot more miles than the PCT itself, then I'd go for them.

Which variants on the zpacks tent (tarp) were you thinking of? It varies quite a bit, and when I hiked the PCT I think that I more often wanted it as a bug shelter than protection against the elements (the PCT is for the most part a pretty dry trail). I note that the hexamid with full bug enclosure is suddenly a lot heavier than the base model. It you're truly happy with just a bug head net all the time, then you might consider a shaped poncho tarp instead. I personally really really like having a bug proof enclosed area at the end of the day.

Another way of looking at this is --- assuming that this is your first long distance trip --- you can't really know how well you'll like it or if something unexpected will push you off the trail. I paid up for a cuben fiber tent (Lightheart Solo) to do the CDT in 2011, but by then I'd already done two other long trips and was pretty confident that I'd get my money's worth out of it. In that context, the ULA Circuit and the TT Notch are really outstanding products in and of themselves. If you find that you like distance hiking, you can always sell your used gear and hopefully recoup some money that way and buy lighter stuff later.
Brian Lewis