-Class rating is a dummy/quick reference/101 guide. Tongue is calc as exactly 10% tow but up to 15% should be safe (there are ways to measure this individually)
-The car's hitch rating is determined by the lowest/weakest link, which is always the car itself (weak chassis, transmission, suspension, brakes, 'what the mfg says', etc.), not the hitch. Fitting a Class 5 hitch on a subcompact car does not automatically increase it's tow. The Mz5 is build on a "compact" car chassis. While it looks bigger and sorta, kinda like a minivan - it is not. They are typically build on mid to full size sedans and are much heavier/stronger framed.
-Keep Archimedes' lever principle in mind! Extenders/Converter/Adapter are ok for tow but I would avoid them for tongue.
-Not all hitches are created equally.
I use this to carry 3 bikes, plan to fit 4 once the youngest bike can fit tube top; it looks like a tight fit. Also, the provided 2--> 1.25 adapter is not desirable. Have to invert it, which leaves very little departure angle. I'm working on making an adapter. It is the only bike on the market that has the unique parallelogram design to allow access to the hatch (with or without hydraulics to assist in lifting). Note the rack itself is 42 lbs! I would recommend the 3 bike aluminum version b/c it is lighter. There's also the "swing away" type racks but they too are really heavy and really aren't meant for Class 1.
http://www.softride.com/rack-products/specifications/softride_dura_assist_bike_rack