Como acotación (aunque ya se mencionó por encima ..) .. ADOdb también tiene una versión "extensión" (tanto para windos pre-compilada como una .dll como para sistemas *NIX) ..
Cita: Speed Up Your PHP Code with the ADOdb extension
Adodb-ext-504.zip provides up to 100% speedup by replacing parts of ADOdb with C code. ADOdb will auto-detect if this extension is installed and use it automatically. This extension is compatible with ADOdb 3.32 or later, and PHP 4.3.*, 4.4.*, 5.0.* and 5.1.*. Source code for all platforms and and binaries for Windows included.
26 Nov 2005 released 5.1 compatible version.
27 July 2005, released 4.4 compatible version.
29 Nov 2004, released thread-safe PHP4 and PHP5 compatible version, with fewer dll dependancies. PHP 5: tested on RedHat8 on WinXP. PHP 4.3.3: tested on RedHat8, WinXP and Win2000.
Fuente .. la documentación de Adodb
http://adodb.sourceforge.net/
Un saludo,