picking mine up next weekend on my refurbished 16" wheels.
i would agree with your expert up to a point. the leggacy runs the cheapest tyres possible all year round, m+s are cheap. its had various makes heros, sportivas,ling longs lol. very rarely get stuck with it in snow, i guess five foot drifts were a bit optimistic. even managed up our farm road in a couple of feet with the space saver on due to puncture. however it runs 185/75/14 or something similar.
my old impreza never got stuck either but it also had canadian snow tyres on, again in smaller 15" size.
i had to stick with 16" to clear the four pot, guess you will have to stay with 17s to clear brembos. i did consider group n wheels to reduce size but they wear out wheel bearings more due to large offset and require centre hole to be machined.
where i would disagree with your expert is the fact that we are likely to be driving in wet weather most of the time. the full blow snow tyres on old impreza i found to be very aquaplaney in standing water.
i was after nokians but was told some of the popular winter brands such as nokian and verstadin were going to be tricky to get a hold of this year due to demand from continent, whether this is true i dont know. was steered to avon winter tyres in the end but have never tried them before so cant comment yet.