Armstrod, I believe that some of the dimensions that you originally quoted refer to different things - the diamond shank (block) in the case of the Dynavector, as opposed to the stylus radii for ZYX.
The shank is what the diamond is cut out of, and has an effect on moving mass and resonant frequency. The stylus radii are what define the shape of stylus, and this affects the surface area of the contact patch with the LP groove, height of the contact patch from the bottom of the groove, tracking ability etc.
Naturally the dimensions of the shank will be larger than the stylus that resides within!
Have to say, however, that the stylus radii quoted for the ZYX look kinda funny to be a Namiki Microridge (which is what Nakatsuka generally prefers to use - certainly for his upmarket cartridge designs). I also use a Namiki Microridge for the Dorian, and the dimensions of what I use are 2.5 x 75 micrometers.
Smaller stylii in general offer superior performance, but are also more expensive to make, and are easier to damage (fracture or failed glue joints). But given proper TLC, they don't wear faster than larger types.
You don't necessarily want to go too deep into the groove because of dirt accumulation at the bottom of the groove (and in some cases the cutting stylus may have had a slightly flattened-out tip, causing an overly narrow and sharp stylus to "bottom out").
Having a stylus with a generous contact patch with the LP certainly does help in reducing noise - vinyl is anything but solid under the pressure of the stylus, and the stylus "floats" on the surface of the vinyl, much like the hull of a boat on water. Groove damage is usually localized, so it help to either avoid it entirely (ny having a stylus that tracks at a different height from the damage), or have a stylus profile that spreads the contact patch out over a wide area of the (semi-fluid) vinyl.
Other things that reduce noise are a low-mass stylus in the cartridge, a tonearm with good bearings and a phonostage that has good HF overload capabilities and low IMD. A low-mass stylus will have a minimum of overshoot when it encounters groove damage, and good bearings in the arm will help to minimize sympathetic resonances from occuring. High HF overload marging in the phono stage is recommended because a record tick is like a natural impulse, with the bandwidth and amplitude both extending quite high. If the phono stage circuitry is not designed properly, hitting it with a high-frequency impulse can trigger ringing which doesn't die down immediately, or you may get intermodulation effects which can be quite obnoxious.
hth, jonathan carr