Opinions - Lowepro ProTactic vs Transit

I've been a Lowepro fan for several years and have bought four or five of their bags during that time. In fact, I have too many at this point and three of them are going to be up for sale later today or tomorrow. Some I no longer use at all, like my first bag -- an Inverse 200 AW beltpack style bag, no longer manufactured, which always sagged even with just the weight of my first camera, a Rebel and two kit lenses. Some are okay, but have generally been replaced by a ProTrekker 400 AW and Transit 350 AW.

Curious for some opinions on Lowepro's ProTactic packs before I plunk down $250 for one...

First, the use case --

For the most part, I do landscape and astro/space photography. I don't do sports, action, or people--I prefer mountains that don't move on me. So I don't necessarily need fast access, although it's nice to have for when I want a little more agility. I carry a gripped Canon body w/ APS-C sensor (when needed, I rent a full-frame body), and several Canon lenses -- two small primes, a macro tube, a 70-200 L IS, and a 2x extender. All lenses have hoods. I have a couple filters, 2-3 extra batteries, and a small & thin waterproof Pelican case that holds 12 storage cards. My 15" MacBook Pro Retina and charging cable is with me almost everywhere I go--and at minimum I must always have the option to carry it when needed. About 50-60% of the time, I also carry a 600 EX RT-II Speedlite and usually only leave it behind begrudgingly for space reasons. Since I travel a lot for my "real job" and my camera rarely stays home, I usually also carry a Canon charger with me. To avoid having even more stuff to lug around, I don't usually bother with my 3rd party dual-battery charger unless I'm checking a bag. Lastly, I need to be taking along a MeFOTO C2350Q2T tripod on almost every trip given the nature of the kind of photos I shoot.

The problem --

I've generally used the ProTrekker for moderate duty, longer distance, or rougher hikes, or anywhere I need greater durability or supreme carrying comfort while moving around. The Transit has been my bag of choice for everything else -- heavy urban use, light duty hikes through national parks or when I don't want to have the massive bulk that is the ProTrekker with me, and for travel photography. It's a great bag, but is lacking in a couple key ways. In particular, the tripod loops don't fit my MeFOTO, which is not a particularly big tripod, and I find the top section of the backpack to be too small for anything more than some cables. Unfortunately, this bag has nothing in the way of pockets or storage other than the main compartment, the relatively small top section, and an extremely small pocket on the front that holds nothing more than a cable or two, or a boarding pass.

I'm looking at the ProTactic 350 AW or 450 AW as a replacement for the Transit's urban and light hike requirements. My ProTrekker is all but irreplaceable for its normal usage, but I'm just not feeling the love for the Transit for how I use it.

I should also note that it absolutely positively MUST be carryon appropriate, including on those small regional jets or turboprops that have smaller overhead bins. On those particularly small planes, I don't care if I need to stow under the seat rather than overhead, but carryon size is a non-negotiable requirement.

Thinking I could probably get away with the ProTactic 350, instead of 450, but I'm wondering if the bigger one would be better to allow use of the extra space for carrying a light jacket or sweater or just having a little more breathing room.

I'm also open to other bags. (Note: I hate messenger style.) And I wouldn't say gerry-rigging a custom tripod attachment would be out of the question, but it's hard to imagine there isn't a better backpack option than trying to force a round peg into a square hole with the current Transit bag.

Any opinions or thoughts on the ProTrekker 350 and 450 would be appreciated, mostly especially if your use case is similar and/or you have used the Transit backpack as well.