This, maybe?
http://lesswrong.com/lw/7k/incremental_progress_and_the_valley/
I'm like 60% sure that its not that article I had in mind, but the idea is the same (incremental increases in rationality don't necessarily lead to incremental increases in winning), so I feel pretty satisfied regardless. Thanks!
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.