I have a spike camp that Ill use for the same purposes you are, that being said, I pack very minimally, and am short enough to get lift with the 22in stays.
Keep in mind the main bag of the spike camp and t3 are essentially the same. The t3's added pockets make up quite a bit of volume.
I was debating the same thing you were a while ago. I chose the spike camp option because I wanted to add whatever pockets I wanted to it based on the situation rather than having them being sewn on and not being used(and I had a t1 so I know what pockets ill use and not use)
Just keep in mind with the late season your getting a much bigger main bag than with the t3.
The dt3 and bikini frame might be an awesome option to look at as well, if you need the load hauling ability and don't mind a stiffer frame. But it sounds to me like you want a little more flex in your pack, which for me was a major point for a day/weekender pack as well. Im loving the flexability of the spike camp with lighter loads that's for sure!
All that being said, if you don't pack very very minimally, you wont fit a weekend into the spike camp. I run a few pockets on mine with minimal loadout to make it a weekend. The late season may be a great option if you like the 1 big bag concept, with the ability to add whatever pockets you want based on if your going for 1 day or 5 days.
I didn't care too much for the pockets on my t series pack, but that's just me. Especially with the modularity of kifaru, I like to be able to add or take off pockets based on what the trip dictates. The Late season with composite stays is also a very light pack, with the same wraptech suspension of the t3.
I think either one of these packs, t3 or late season, will allow you to get the flexibility you want, with the load hauling capability. It about wether you want a 1 big bag pack, with the ability to add any pockets you want, or a pack with built in pockets.
As per the double layered bottom on the t3, and not the late season.... you may want to call and check on that one cause my spike camp has a double layered bottom.
Someone can correct me if im wrong...... but the t3 and late season have the same exact suspension and load hauling capability
Now the DT3 has the beefed up suspension of the frame sheet.
The spike camp has the Omni suspension, which cannot handle heavy loads as comfortably as the wraptech that's found on the t3 and late season. The spike camp is also only available in 22in stays, which is a big turn off for most guys who are not short like I am.
Hope this helps a little, I went through the same decision a while ago.