It depends is the simple answer.
There is quite a good table that Nigel Rolfe put together on the web site.
You are in the regions that overlaps quite well between 7 and 9. I'm only 73 kg but sail a 9 mostly in the summer. However if the wind is forecast to be 15-20 knots I'm better in a 7. FWIW I usually enter as a 9 but check the forecast just before the event starts and if there are forecast some strong days I'll drop down to 7. For club sailing I think I've dropped down twice this summer, but if you look at windy open meetings you will see people make rig choices.
End of Season open last year and
Island Barn open this year not a single 9. We all dropped down. Once it is consistently over 20 knots almost all the 9's drop to 7. You CAN sail the 9 but it is hard work and you go faster upwind in a 7 (especially for us mid-weight sailors).