Stiffness: I found them to be every bit as stiff as my TLT5P without tongues(carpet test, locked in skis), in fact a bit more stiff, but not much(I think this is mostly due to the fact that I can make them tighter on my chicken legs.
Sizing: I can go down a size to 25.5 shell(277BSL). I did a shell fit and found the 25.5 fit comfortably. I didn't feel toe pressure in a 25.5, but the forefoot volume is a little low. Whereas in the TLT5 26.0 I have to tighten the instep buckle more than half its range, in the Spitfire 2.0 25.5 I am on the loosest edge of the instep buckle range. In the TLT5P I use the felt pad under my Sole thin footbeds to take up volume. In the Spitfire I was using my footbeds, but nothing else to take up volume.
Climb Mode: The range of motion is significantly better than the TLT5P with CL liner. It is both greater range and with less friction. Rearward range of motion can be obstructed by the ski mode exoskeleton catching on the rear of the cuff, but after a few times going through the motion that seems to clear itself up. More on the mode change and exoskeleton later. I didn't notice any heel slop when in ski or climb modes even with the instep buckle loosened(this is likely due to inattention and non real world testing conditions).