As we are doing more & more Excel output generation, this became a bigger and bigger problem. At first we've tried solving the problem via a newer PHP based Excel library, PHPExcel. Unfortunately, it is massive beast, that is not only slower than the old Spreadsheet Excel Writer/Reader, but memory hog too. [...] So, I turned to Google and found LibXL, which is a small, C++ (with C, C++ interfaces) library that promised really fast Excel reading & writing.
His extension gives you an object-oriented interface to the library that can generate Excel files with a lot less resources than some of the other PHP Excel extensions out there. He includes a sample benchmarking script he used to generate these stats.