Sometimes when you have too many products it is difficult to generate a good feed due to timeouts or server restrictions.
The Any Feed module resolves this by proving partial outputs through URL parameters.
You can use the parameters &start= to determine the starting product for the feed. You can then use &numResults to determine the number of products to display.
This way you can make smaller feeds that cover your entire product base:
Generates the first 1000 products
Generates a feed of products 1001 -> 2001