Etch rate of SiO2 in Buffered HF is about 960A/min.
Etch rate of SiO2 in 1:10 HF is about 360A/min
Etch rate of SiO2 in KOH depends on temperature and solution contents. I don't
know what is the etch rate in 20:80 solution, but in 40:60 solution at 80C the
etch rate is about 55A/min.

Best regards,

Andrzej Prochaska