The high pressure high temperature synthesis (HPHT) use pressures from 5GPa and up, but as the slides talk about 600MPa as a useful pressure the difference is "

The high pressure high temperature synthesis (HPHT) use pressures from 5GPa and up, but as the slides talk about 600MPa as a useful pressure the difference is "only" a factor 10. One additional issue with diamond synthesis with the HPHT is that you need 1400°C, and the correct mix of graphite and metallic catalysts.