That being said, the scenario you provided isn't quite the same, so I will slightly modify it here to make it more similar, in order to demonstrate a point - counterpoint discussion, as this is a thing where right and wrong aren't always precise and clear.As a young man, you are dating that beautiful girl, and you decide to let her go (you have the cash in hand, but decide to pay down the mortgage by giving up the cash).

I say, not exactly, but it is a good starting point, particularly for beginners to keep them safe and make the numbers simplified for calculation purposes.Using any "average" particularly across the country, is not precise or relevant to a specific given local area in one part of the country, therefore, the rule (or guideline to be more descriptively accurate) must be amended on a case by case basis - per investor skill level, per area, per size and rent level, etc.

Its not used because, and at least from my limit experience, I've never come across two investment that had such similar characteristic that I needed to get that level of precision in my measurement.

They also have rent controls and strict rules on precisely which forms you must use to serve notices. 

I cannot tell you precisely what the current market CAP rate would be in that class of property - namely because I care little about CAP rate when underwriting - but sales of slightly larger buildings (15 - 30 units) have been down in the range of 5 - 6% over the past couple of years.Nothing a small hike in interest rates wouldn't help.Moncton is a little more varied.  

I also buy real estate & other hard assets like oil & metals precisely because they can serve as a currency of their own & protect me from government & the dollar.Cryptos are in their infancy & I understand your skepticism as they have a long way to go & will become hard asset backed like a gold standard after the next crash.

Precisely.

Your situation you are describing is PRECISELY the niche I work in - scaling small residential or multifamily portfolio's accordingly.

And then lending rapidly decreased, precisely when those properties were being foreclosed. 

It's precisely because they only do it once a decade that they obsess over it.