typical value of contact resistance: 1) banana connector, 2) solder joint
10 m&Omega; for a full-size banana jack sounds really high to me.  However, the obvious things for you to do are:

Measure it.  Put a known current thru the connection and measure the voltage across it.  This will tell you what you are actually getting, not the worst case it could be.

Look at a datasheet.  Find a reputable company that makes banana connectors and see what they rate the maximum contact resistance as.



These things should have been obvious, and basic research you should have done before asking.

As for the solder joint, there is no mechanical "contact" there, and the problems associated with it.  It's just a solid metal connection.  Most likely the weak link is the copper trace on the board after the solder joint.

For starters, analyze a solder joint as if only the copper were present, but directly connected.  In a proper solder joint, the copper parts are touching anyway.  Solder has higher resistivity than copper, but there is also a lot more of it in parallel around the joint.  The gap between the solid conductors is also very small.