I'm not sure about this forum because right now it says the most ever here was around 450. I hope that's just 2012. I thought I remembered at least 650 people in this forum around the J-20's emergence. I think there was like well over a thousand in Key Aviation at the time.
I was talking about CJDBY lol. Sinodefence had seen better times. When the J-20 came out I think it was around the number you reported.