php.ini directives

New PHP 5 configuration directives:

realpath_cache_size integer
Default: "16K"
Determines the size of the realpath cache to be used by PHP. This value should be increased on systems where PHP opens many files, to reflect the quantity of the file operations performed.

realpath_cache_ttl integer
Default: "120"
Duration of time (in seconds) for which to cache realpath information for a given file or directory. For systems with rarely changing files, consider increasing the value.

To perform compress at the server level under Apache see: How to enable Apache compression with mod_deflate

output_buffering = Off
output_handler =
zlib.output_compression = On

XOR (try this one)

output_buffering = On
output_handler = ob_gzhandler
zlib.output_compression = Off

Require setting:
include_path = "." (Example on Windows:  include_path=".;c:\php\includes")

extension_dir = "E:/php5/ext"

upload_tmp_dir =E:/Tmp/Apache/Php5Upload

cgi.force_redirect = 1 (Default if undefined, the only case to set is with IIS, in this case use cgi.force_redirect = 0)

[PHP]
;Detail about each directives, see the php.ini-recommended in the PHP distribution
engine = On
zend.ze1_compatibility_mode = Off
short_open_tag = Off
asp_tags = Off
precision = 14

You can turn persistent database connections on/off from your configuration file php.ini.
For MySQL:
mysql.allow_persistent = Off or On

It is difficult to see any difference in the speed, for me. If the speed seems the same turn it off.
This settings can have a direct correlation to the MySQL connection settings.

short_open_tag = On (might be needed to run VBulletin)

--------Other interesting values------