I'll be doing cold water diving in northern canada as well so that's why I was thinking about the high end set up. Is there much difference between the MK25 and 17?
There is a huge difference between the MK25 and MK17, MK17 being more suitable for cold water and although they are a bit cheaper they are not less high-end regs.
MK17 balanced sealed diaphragm with a dry chamber, no internal parts are exposed to the environment.
MK25 balanced piston with wet ambient chamber, the water stays in the chamber at all times and if frozen will cause the regulator to freeflow, especially if the reg is exposed to the outside freezing temps.
As you are a new diver and live in Canada and this is your first! and probably the only for sometime regulator in your shoes I would definitely go with MK17 as it gives you more margin for an operator error in the cold water.
MK25 needs to be treated carefully in water with a temp below 40F. You need to have a good cold water techniques to dive it in cold water especially when the temperature is freezing outside. If improperly handled pre dive in those conditions the chances that MK25 will freeze are way greater.
Myself I have started diving MK25/G250V this season in temps around 40f and so far they were behaving great. When I started my diving I bought a diaphragm reg (Zeagle FH6, similar to MK17) and as my techniques were far from being any good I managed to get even a dry diaphragm regs frozen
I bought my MK25s because I love how they route on doubles. I still use my diaphragm regs (Zeagle FH 6) for the very cold season.
MK17/G250V is an outstanding regulator and you will unlikely grow up from that combo and will unlikely regret purchasing the one. My buddy has been diving his MK17/G250V from day one and never was disappointed, he now has 4 sets.
