High Speed design rules for 10GHz
It depends.

In Microwave engineering, we often say we are dealing with "RF" when you are working with devices and interconnects that are longer than a few tenths of a wavelength. At this point, classic nodal and lumped element analysis no longer works, and care must be taken to include distributed effects, work with transmission lines and think in terms of reflections and S-parameters. 

In other words, when making a large system like a industrial machine or communication network, it could be that a MHz is already "high speed". But when working on-chip, even at 10 GHz, we might be able to work with lumped inductors and capacitors, as they are still very small with respect to the wavelength.