WesTexDiver:If the OP was going to dive in Ice water and Contaminated water then no doubt the MK17 would be choice over the MK25. However, The MK25 is a cold water regulator WITH anti-freeze protection. The X650 is not the smallest 2nd stage in the world, and then again it's not the largest. Again if size were an issue then possible he would have mentioned the fact that he wanted a certain size or look, in which case there are several other options. To quote the 2007 catalog, " The X650 is the best performing second stage of the SCUBAPRO line as it requires 20% less exhalation effort than any other 2nd stage, because of it's unparalleled air flow characteristics." I have dove in cold water to depths over 100 feet several time, I knew I had a superior main rig the first time I had to switch from my main rig to a stage bottle on my way back up at 50 feet. It wasn't exactly labored breathing, but it sure made me appreciate the way the 25/650 set up breathes. Just my 2 cents. By no means do I consider myself an expert, was just wondering for my own curiosity about some of the other recomendations...Cheers and see ya below.
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