getTime() Accuracy

So, the results are really promising with little or no more shift with:
E.setRTCPrescaler(320000.923(1+466.385/46190))
The pico is still ahead of gps time by -1.42972660064 s / 4215 s.

Note that those figures are now not really meaningfull: The time granularity on gps time and pico's time are 1 second each...

So now, more test, more or less at room's constant temperature with:
E.setRTCPrescaler(320000.923(1+466.385/46190)*(1+1.42972660064/4215))

Finally, there is the prescaler granularity too..