@Doctor Rig
On design
The Deep6 Signature second stage, like just about everything out there now, is based on an old Scubapro design which has evolved into the G260. This is a balanced-adjustable second stage that is designed to be the highest performing on the market.
The C370 is also a balanced adjustable design, but is not as high performance as the G260/Deep 6. Nothing wrong with it, but it's not a regulator I'd take really deep, under the ice, etc etc.
Deep6 first stage is an evolution of the Apeks DST design. It takes a form factor more similar to the Scubapro MK25 which allows the bottom turret to rotate freely with hoses on it *not really useful in the water, but convenient during setup*, and looks a bit better IMO. The 5 port swivel turret gives you the most flexibility and freedom with hose configurations and routing whereas the MK11 is similar to the Apeks DS4 and is a very basic regulator. Again, nothing wrong with it, but it's not nearly as good.
D6 is environmentally sealed which is ideal for cold weather diving *note not just cold water, if the air temp is near freezing the first stages like to freeze up at the surface*, and it's also ideal for all diving overall since it does not expose any internals to the water *ideal if diving with any particulate in the water, especially salt*. The MK11 is not something I'd take in any sort of cold water and is also a regulator you have to be diligent with when diving in the salty stuff.
Realistically these are kind of apples and oranges regulators because the Deep6 is designed to compete with the highest end regulators on performance and features, while the MK11/C370 combination is a basic model regulator designed for travel divers.
On performance. Unless you are a diver who is experienced with a lot of different regulators, it is highly unlikely you'll be able to notice any significant difference in performance between the two. For recreational diving the Scubapro setup will perform incredibly well for you, but the Deep6 has the potential to perform better.
@cerich has a huge background in regulator design, is an avid technical diver and instructor, and did a truly outstanding job with that regulator. It is in my opinion one of the best regulators on the market today and it certainly is the best value in regulators out there today. If you want a regulator that will grow with you and truly be the last regulator you NEED to buy, then the Deep6 really is the best choice out there.
