I can give you some insight on the catalyst.
The volume of the pack is perfect for longer trips. It held all my clothing and equipment, including a 2 person tent, and bear canister for 3 weeks on the JMT. Nothing was on the outside of my pack other then water bottles, tent poles, and misc little gear ( p00p trowel, pee bottle etc). All the major stuff was inside the pack. I can't comment on the bottle loops as I just store my water bottles in the side pockets. The side pockets are cavernous and can hold 2 bottles if needed. Plus I use platys so they are incompatible with the shoulder-bottle holders. There is no option to add a lid to the catalyst. The lack of the top cover did not bother me at all. Some people hate the roll top--I don't mind it at all. Yes it takes longer, but the added water protection kept my mind at ease during downpours. Often times I would start my hike wearing an insulating puffy (it was like 30 degrees in the morning)and after I warmed up, I would just shove my puffy on the top of my pack, and roll the top. My insulation always stayed dry, even during rain. It beat having to take my puffy off, digging out everything in my pack to take out my liner bag that held my sleeping bag and clothing, and putting the puffy in there. Quicker for my on-trail costume changes. Yes it will carry 40lbs if needed. The frame will handle that load, but user comfort is personal and dependent on conditioning, build, etc. 20-25 lbs was a dream to carry for me. When I went up to 30-35 lbs after a long resupply, I still didn't suffer from sore hips or shoulders, but I was tremendously slower in speed :) I dont use a CCF, nor does the pack require one to make a frame. If you use one b/c you don't own an inflatable, I guess you could strap it across the very top, using the the single compressing strap that goes over the roll top.
I don't own the GG blaze, but I own both a GG nimbus meridian and vapor trail (predecessors and the foundation of the GG blaze) so I can make some general comments. The volume of the 2 packs is very very comparable. The GG might have a slight edge on the catalyst, as the bottom is wider on the GG. But I would not let volume be the decision maker between these two packs...the difference between the two is almost impercievable. The nimbus meridian has a beefier suspension than the AC suspension on the Blaze series. Even then, the nimbus suspension was not as comfortable as the ULA catalyst suspension for me...therefore I imagine the AC suspension would be even worse for handling heavier loads. Because GG now adopts a Molle/PALS military style webbing connection system on its hipbelt, tons of aftermarket pockets will fit, so that should be of no concern for you. \
I read that another user had shoulder chaffing at 35lbs with the catalyst, which brings up a good point. I find the catalyst extremely sensitive to how you load the pack. Weight needs to centered and packed well for this pack to shine. One day I had shoulder rubbing at 24 lbs. I didn't understand why until I reopened the pack to check how I packed the contents. My bear canister was off center that day, so one shoulder strap was taking more of the load then the other. Once I rebalanced and repacked, all was good.
As a general note, if you find the volume to be lacking on either pack, I would highly recommend that you submit your gearlist to BPL for critiquing. I'm saying this with the most positive intentions. You can probably shave a lot of volume and weight after letting everyone scrutinize your gear. Good luck!
PS: if you really really want a lid that converts to a fannypack, look at the GG nimbus meridian. But again, I did not think the suspension was as comfortable as my ULA catalyst.