The spare pressure is set for 44 PSIG because it is a low speed tire intended to be used on a temporary basis. I believe the max speed allowed on it is 50MPH or so due to less layers of rubber and little to no steel belting.
Ordinarily yes, space saver spares are built differently. But I think the full size spare is a standard steel belted radial.
I believe the full size spare is spec'ed for 44psi to compensate for the taller sidewall. The extra psi brings it up to the 17" 40 series sidewall flexing properties.
I would run your winter tires at 40PSIG on the street to start. This is what I run mine at and have had good luck with both wet, snow, and dry performance. If going fast in the dirt, you'll want to run them close to the max pressure (~ 50 PSIG) as to prevent de-beading.
I just installed my steelie set up and immediately hated how it felt; I jacked up the fronts to 45 and rears to 42 (5psi over what I normally run with the stockers), and am much happier now.
I know this somewhat defeats the purpose of taller sidewall for winter, but I felt like 75% of the car's charm was being lost. I will deflate accordingly for any snow/rain storms. As I live in a quickly plowed area (NYC, Long Island, NJ), dry performance is important to me.