[repiret]

I would argue that neither of those things are metrics to measure for a transistor, since they are affected by how its used. Properties of the transistor itself are what matter: size, drain and source capacitance, leakage current when off, drain-source voltage drop when on, and probably a dozen things I don't really know about.

[tspiteri]

The properties you mention are mainly "low level" properties, which in the end affect the "high level" properties that are speed and power consumption. For example capacitance limits clock speed and also has an effect on power consumption, and leakage current reduces power efficiency. Capacitance and leakage current themselves depend on size. I think that the physical properties you mention (and maybe others) may be used to create a model, which can then be used to estimate clock speed and power consumption at different operating points.