I have "number of posts to display" set to 9999, I want to see them all. No idea how many I have exactly (might be nice if MarsEdit could tell me :) ). When I sort them by category, scrolling is very slow. When I sort by date it's very fast.
I'm not suprised that the performance tuning hasn't been a priority at that level of posts-syncing (since the recommended number is closer to 30!).
But I would like to see MarsEdit move toward obliterating the "sync limitations" ... so I am definitely interested in optimizing the high-quantity posts situation. I'll see if I can simulate this in my test environment and figure out what is causing the slow sorting.