I'm speculating here, but as the SXM board requires higher amps than dna, shouldn't that play a role in how hot the device gets?
I have a Raytec thermal reader. I just did a test on both devices.
Freshly charged batteries in both mods. I puffed 30 times on each, same way I normally vape, about 2-3 sec puffs but with a 2-3 sec pause between vapes. Ambient temp is 85°F (yeah, it's hot in NJ). Both mods and atomizers were 85°F at the start of the tests. I held each mod with my finger tips with the least amount of contact as I could.
SX Mini M - KF4, full tank of juice (Lenola Cream), 28g Ni200, .10Ω, 20j, 380°F. The KF4 became warm as usual, 100°F at it's hottest point (I took readings top to bottom). The SXM at it's hottest was 99°F at the display and 93-98°F around the body. The c-frame was hottest at the screen, not near the atomizer or at the battery cap. Makes sense since the SX350 board has a coil there. On the side of the SXM, it was warmest at the center of the mod by the screen again.
VS rDNA40 (no sharkskin) - KF4, full tank of juice (Honey dew/pear mix), 28g Ni200, .12Ω, 20w, 430°F. Similarly, the KF4 was 100°F at it's hottest point. The rDNA was 94°F at it's hottest point, just around the atomizer base. 89-93°F everywhere else.
This confirms my experiences. Like I said, the SXM isn't uncomfortably warm to hold but it is warmer than the VS or other DNA40 mods I own when vaping as I normally do. I'm actually surprised it wasn't hotter and there was only a 5°F difference.