I struck out with APC after trying a few times and not succeeding. Fortunately, I was able to find XCache, a comparable PHP opcode cacher that had one big advantage: clearly written directions on how to install XCache on OS X. In my case, I was installing it on OX Server, instead of OS X, but it looks like the instructions work on Server as well. After installation, to avoid any glitches, I tried disabling wp-cache2. Speeds looked good after that, so I tried enabling wp-cache again. Performance actually went down when I enabled it, so I disabled wp-cache2 again. I think I’ll leave it disabled, and see what XCache can do on its own. So far, it’s definitely snappier.