I'm sure others will chime in, but I believe 12# is the lowest recommended for the 92 platform from a reliability standpoint, although in a competition setting (versus potentially defensive use), you could go lighter chasing an even better trigger.
From LTT: "**If purchasing for the 92, we recommend using the 11# hammer spring for competition only. We do not recommend the 10# hammer spring for the 92/M9/96 series pistols at all**"