Upper layering System-thoughts?

Since you already have the DriClime, this comment won't be much use to you, but…I had a DriClime for a while and eventually swapped it for a Montane Aero Smock (83 grams) plus A Mont Microfleece pullover (276 grams)

http://www.gearbuyer.com/products/montane_aero_smock_wind_shirt_mens.html
http://www.mont.com.au/index/catalog/product/037

The weight difference is minimal, and I found I preferred the versatility to wear the windshirt alone on days that were windy but not too cold, or walking up hills-the driclime was just too warm in these situations. This combo is also warmer than the DriClime when worn together.

As for vest…flip a coin. Again, I once owned the flight vest, but found I just about never took it on trips since my MontBell UL inner jacket was so much more versatile for an extra 40 grams. I haven't used the flash vest.

Having said all that, lots of people love the items you've listed, so it looks like you can't go wrong.

I'm an O2 fan as well…shame I'm allergic to wool :(

That looks like a nice system, I think it would work well. The Driclime windshirt is a nice piece of gear… my daughter lives in hers as do many people. That said, I don't use a driclime shirt, I use an unlined windshirt because the lining makes the driclime means that I can only use it in cooler conditions. Since you are hiking in a short sleeve shirt, this might not be as much of an issue for you.

I am with you on taking a vest. Especially if you have the driclime which will keep your arms warm enough. Keep in mind that the Flight is SIGNIFICANTLY warmer than the Flash. The flash would be enough for me, but some people like the extra warmth. I would boil in the flight. If you go with the Flash, consider a neck gaiter since it's a V-neck. I prefer synthetic high loft clothing… especially in OR and WA.

The one question I would ask is what you are doing for sun/bug protection? Some of us hiking in long sleeves all the time to minimize the amount of lotion that is needed.

My system (be used on many sections of the PCT) is:

light weight powerdry zip long sleeve
patagonia houdini
montbell thermawrap
dropstopper rain jacket (or rainshield o2 cycle jacket)

In hot / buggy conditions I would add the rail rider adventure shirt which is a long sleeve shirt with side vents for protection against sun and bugs. I wear it during the day, wash it each night, and sleep in my powerdry shirt.

–mark

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Here's what I'm thinking of bringing. I tend to run on the cold side, but I'm thinking that I'm overdoing it for the top.

Smartwool/icebreaker base
Patagonia R1 hoody
Rei powerstretch pullover (only for colder sections)
Marmot Ion windshirt
MTN Hardwear compressor
Arcteryx alpha SL

Plus a lightweight short sleeve hiking shirt.

I'd add to all the good advise above that it's important to keep a separate sleeping shirt. It helps keeping your bag as clean as possible which is particularly important in such a long trip. You probably don't want to wash it before you get home. Maybe you can use for that one of the two shirts in your list but I see one is short sleeve. For sleeping, I'd take the lightest long sleeved I could find. On the PCT I used a silk shirt that was around 100 gr. I'd only use it for sleeping or laundry time but it's always there for emergencies too so I'd only take one hiking shirt.

I'd also like to second Mark's and Allison's comments about the sun/bug protection (long sleeved shirts are better for this) and the convenience of keeping windshirt and insulation apart for maximum versatility but I understand these are very personal things. In general, your kit looks good. It'll work.