I think I found some inaccuracies in the LPC11U6x user manual Rev. 1.6 dated September 6th, 2016.
In the section on the Systick timer (section 24), 24.2.2 states:
"The system tick timer clock is fixed to half the frequency of the system clock."
However, the block diagram below this in Fig. 85 shows a multiplexer that allows to select the base clock using the CLKSOURCE bit in SYST_CSR. I'm still waiting for the delivery of actual hardware, but try to write some code already. Can anyone confirm that the CLKSOURCE bit actually toggles between full and half CPU clock frequency as base for the Systick counter?
In addition, section 24.2 refers twice to table 452 - correct would be table 349.