For serious offences (which include speeding +40km/h above the limit) it is not an automatic penalty, nor is it up to the gendarmes. It is a matter for a judge to decide so basically, yes you will have to wait until it has been to court and judgment has been passed. That’s the procedure, seems clear enough? although obviously the timescale isn’t set in stone and will vary in each case depending on all kinds of outside factors beyond the control of the gendarmes. Sometimes the judge’s decision will have been made within the 3 months and sometimes it won’t, no doubt it is a tad annoying and inconvenient for the offender to have to wait but if the court has a backlog there isn’t much anyone can do about it. I imagine the courts will have spent September catching up after the summer break during July/August.
Have you enquired whether a date for the court hearing has been set? If not there is no guarantee that the decision will have been made within the next 10 days. If it hasn’t you will not in fact “know either way”, you will have to carry on waiting to see what the judgment is, but once your administrative suspension period is complete you will be able to drive again while you wait to find out the penalty.