I think I speed up a little bit maybe 10-50 posts before a major milestone. Then I pause on the final one, because I don't want to waste it on a boring everyday thread. I usually wait until I have something clever to say in MD or MO. Which can be pretty rare, as many of you can attest. I think once I even delayed posting my milestone post by half a day or so just to annoy Map, because I was pretty sure she was waiting for my post so she could post congratulations.
I actually find the opposite, that it seems to take longer once you get to that last 100 of the K mark. Where the first 900 posts go by quickly, because I don't notice the post count at that point. But when it gets to 900+, then I notice and that slows it down. I don't purposely slow down or speed up.