If you suspected maybe WordPress and other PHP apps were slower to ping/trackback sites and other fetches under CentOS 7 than CentOS 6, you aren’t imagining things.
Apparently libCurl (and therefore Curl in PHP) has been broken for over a year now without RedHat applying the available patch and pushing an update.
patch: https://github.com/bagder/curl/commit/d529f388 (note July 2013)
2015 UPDATE: new wiki page for HHVM on CentOS7 with alternate instructions
While building HHVM (HipHop Virtual Machine) for faster PHP on CentOS 6.x was pretty much a nightmare because almost none of third-party libraries are available from major repositories, the freshly released CentOS 7.0 solves most of this problem as it has far newer packages available from EPEL (because it has roots in more modern Fedora 19).
Note that unlike PHP/PHPNG, HHVM requires major resources to build. You may be used to making PHP in 15 minutes on a little old 256mb 1ghz box. You can forget that with HHVM which is a beast to compile. 1gb ram minimum and lots of cpu power required to keep it an hour or two (this is part of why PHP NG instead is so exciting because it will be so much easier to custom build).