Now, I'm no expert, but if the cable is coming from a pole about 50 feet away, and to that from a cabinet well up the street, would another 20 feet or so make the signal so much weaker?
No, it would probably make little difference, but...
Could you not have the cable dropped into your loft, with master and router located in the loft? From there you would be able to run cables to where ever suits and it would give you wifi coverage with a better spread throughout. Nothing to stop you running a CAT6, from there to a second repurposed old router, for even better coverage.