Need your opinion - 50% rule

[Carlos Lopez]

I'm new at real estate investment and have been reading everything I can on investing properties, specially at Bigger pockets. My goal is long term investment. Buy and hold. Being so new I would the more experienced opinion of the wiser BiggerPockets community.

Here is my dilemma:

I live in Northern California where house prices have hardly dropped and my community has currently 1 house below the $400,000 price.
We are near a University and the rental market is always busy.

I'm currently looking at two houses.
A Duplex that rents for a total 1700 / month
A Fourplex with rents that total 3950 /month

The duplex, I'm thinking of offering 215k bank wants minimum 235k

Fourplex I was thinking of offering 400k Banks wants 465k

At these prices my calculations don't seem to cover the 50% rule.
I'm doing FHA or Conventional with only %5 down.

Doing my calculations, at the prices they are asking I don't even get a Cap Rate of 6% or the 1% rule.

What do you guys think? Houses are so expensive in this area and this makes it difficult to negotiate using comps.

I'll appreciate your input.