I can't say this from experience because my own consistency hasn't been the best but I can say that logically to sustain 25 you would have to aim for 27-28 in case of times you can't post or you'll be dropping below 25 all the time.
You are correct. At my best I was close to 25 and then I left. It dropped quickly. And the thing is, to rise gets more difficult because where thirty or forty posts in day makes huge influence when your average is fifteen, when it's close to twenty five it barely nudges the needle. Math is math after all.
I am happy where I am and I do post a lot here and there. Staying at 25 per day is not easy and over time it will go down. Some days it is easy other days not so much. As long as you are active and work to stay ahead of me you should be good .
When I was first here a new member I was posting like Abnninja and was somewhere between 25-30 posts a day. I was every where posting on everything giving my opinion on things. I was working nights at that time and enjoyed having something to do. Then life took a turn and I took almost two years off or maybe three as I was moved to day shift and had to reassess my life and then find the time to get back here.
It took me a lot of time and effort to get to where I am now. I believe back then I told Jay that I was working to be the top poster over all. I knew I had a lot of ground to cover and I did rise quickly. It was interesting to say the lest and I got a lot of visits from the moderators too. I think I am still high on their lists to watch .