Average train speed across Europe. 123.7 mph in Spain and 121.7 mph in France.
At the moment I believe the fastest journeys in Europe are Paris-Strasbourg (246 miles as the crow flies, with the fastest train journeys scheduled this week taking 1 hour and 45 minutes), and Paris-Bordeaux (309 miles as the crow flies, with the fastest train journeys scheduled this week taking 2 hours and 8 minutes). Madrid-Barcelona, which is 312 miles as the crow flies (i.e. almost the same as Paris-Bordeaux) takes 3 hours and 2 minutes in the fastest trains, so the map above might overstate the average Spanish speed (due to the fact that the Spanish rail network is made up essentially of high-speed lines, with fewer traditional lines compared to France which had a more developed rail network than Spain).
In terms of mph, the Paris-Bordeaux journey (which is longer than a straight line between the two cities, as the railway line deviates somewhat from a straight line) is accomplished at an average speed of 156.4 mph and the Paris-Strasbourg journey at 155.5 mph (both with top speed of 199 mph, but the entire journey has a lower average speed due to sections that are slower + urban sections at the beginning and end of the journey).
In Spain, Madrid-Barcelona journey is accomplished at an average speed of 127.2 mph (a bit underwhelming, but I suppose they have decreased the speed due to the recent accidents in Spain), and the Madrid-Valencia is at an average speed of 130.0 mph.
So Paris-Bordeaux is currently the fastest train journey in the western world, and perhaps in the entire world (unless there's a Chinese journey accomplished at a higher average speed, but that's not certain considering how they have decreased the speed of their high-speed trains to save money).
Compared to California, downtown SF to downtown LA is 347 miles as the crow flies, so if it was built and operated like the Paris-Bordeaux line (i.e. actual rail line not deviating too much from a straight line + operating at an average speed of 156.4 mph), it would take 2 hours and 24 minutes to go from downtown SF to downtown LA.