Google Sitemaps limit / memory usage

Hi all,

I've just set up the Google Sitemaps generator, and it seems I have 2 problems :

1) Sitemaps is timing out , even with allowing 256MB memory usage
2) Google sitemap has a limit of 50,000 pages afaik

Currently our catalog has around 110,000 products across 1800 categories.

What would be the best way around this issue - is there a way to limit the sitemap to 50,000 pages which in turn should reduce memory usage too?

Our Google merchant extension, which includes sitemaps has the option of splitting the feeds