Last week I had a few problems when I was trying to export my Magento Product feed with 10k products for Google Shopping. The script kept timing out and giving me Fatal error: Maximum execution time of x seconds exceeded warnings. I tried changing the php.ini parameters like max_execution_time, but no luck.
Once I switched to the Feedonomics API, exporting a Magento feed with thousands of products for Google Shopping was easy, because it took care of implementing the database logic in a scalable, and it worked flawlessly. Better yet, the Magento export took only about 40 seconds.