I've been planning on getting a Clark for some time now (which of course means saving up) and noticed that they've released a tropical version with the spreader polls. Initially I was sold on the NX model but as it's generally easier to add insulation rather than remove it I'm looking into the TX version as well. Since the TX bed is flat, or at least devoid of pockets under the torso, I'm guessing it would take a 1/2 or 2/3 underquilt well or even just an additional nylon layer to act as a wind barrier similar to how the NX pockets would work. (Oh dear I was trying to escape DIY projects by getting a Clark in the first place...)
I will be out when night temperatures are in the high 70s to mid 20s fahrenheit and was hoping for any advice from current owners. I'd also really appreciate comments from you guys that have both models about what you like and use with each.