If you are going to shake, rather than stir, a Martini (yes, it then becomes a Bradford) then this 10:1 ratio works rather well as there's something about...
Agree, cold is key! I was fortunate enough to have some liquid nitrogen which I had sourced for a sorbet I was making for a "gourmet" dinner I was cajoled into cooking. As per Dave Arnold's instructions I chilled a glass albeit to excess (the martini actually froze to the sides of the glass while the stem remained room temperature!). Absolutely amazing.
Have you tried the Frozen Martini? It goes into the freezer for 4 hours, but has a bit of saline solution (I use a pinch of salt). Put the glasses in the freezer at the same time. WONDERFUL.