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I have a Aqualung SolAfx 8/7mm semi-dry and it is great in upper forties on up but I did get cold diving lake Superior with 41 degree temps. Gaffer
I just tried my new Whites Fusion drysuit for the first time this past weekend and will not be using my 7mm anytime soon. I could barely feel the temp changes at the thermocline except for the exposed skin on my face. From now on, my way will be the dry way.
I dive a Simi 7mm suit and have made 1h8m dive in 51* water and was fine other than my feet, but that was my fault for grabbing the wrong booties. I will be going Dry for the next suit.