Go for the t4, the t3 will only take one large cot because it needs to be in the middle of the tent. I have an 80" x 33" cot and it fills up the t3 pretty good. An 84" cot would never fit IMO. Buy once and be happy you did.
Thanks for your thoughts! It sounds like I need to decide if we're going with two big cots or Exped double wide mattress. If it turns out the Exped mattresses are as good as everyone says, the smaller packed size of the T3x is likely going to outweigh having room for two cots.
My thinking so far....
The price diff between the two is a non-issue (I'm actually kind of surprised how cheap these tents are). The extra standing height of the T4 is nice, but mostly a non-issue (I'm tall but used to crouching). The packed hugeness of the T4, however, is an issue, both physically and philosophically. I have what I consider a huge rig (1st Gen Sequoia). The t3x will fit inside crossways behind the middle row, but without much room to spare. Coming from a human-powered backcountry experience that in-the-bag-largeness blows me away. So the fact that the T4 is so much bigger and either has to go the front to back (which messes up my existing organization system) or on the roof is a huge negative to me. Sure, I could *make room" for it, but philosophically, I just don't want to have so much stuff in my rig or campsites or basement.
I realize it's all a juggle. Though 'm used to having a small, compact kit, I'm getting older and more sore, and less able to sleep (and enjoy myself) when I'm not comfortable. As I move to a more vehicle-dependent mode of travel I'm really trying to balance that desire for comfort + my ability the bring it
all along (curse of the large rig) against the "small, compact kit" way I remember my younger self. Back in the day, I'm sure I held some disdain toward those guys with the overstuffed truck and the giant campsites. Thankfully the disdain is long gone (I've "walked a mile" in those guys' shoes. Everyone has different needs. Do what you need to do to get out there!) but my desire keep the kit and campsite on the compact* end of the spectrum remains.
*definition of
compact TBD. In a couple years I'll probably have to come back and edit this post to talk about how I got a bigger rig to bring more stuff ;-)