Enable WP-Cache + GZIP
For normal users, the big bottleneck is the size of prototype.js, and it is most unlikely change unless major version update. So let’s gzip it first and check out the performance boost: Using Dojo ShrinkSafe, the prototype.js is cut to 49K, not bad.
This helps me to save tens of kilobytes, now the gzipped-shrunk protoype.js is 14.6K only, the overall improvement is gzipped 30.2K versus original 142.0K, that is quite impressive.
Use client-side cache
mod_expires just did the right work, load the module and enable it wherever the content would not change:
ExpiresActive On ExpiresDefault A2592000
Use these directive to disable ETag globally in httpd.conf:
Header unset ETag FileETag None
I get B(87) with cache, A(95) without cache in YSlow performance score. The next step optimization may introduce CDN service, for example, Amazon S3.