I am redesigning a website that offers free web pages to users. Each of the estimated 100,000 free web page has a link on it to our homepage. Currently, the user pages are displayed using the same domain name as our main site, but we're considering separating the member pages onto their own subdomain. So, my question is... which will give our site a better ranking in search engines to separate or not seperate?

If we seperate, there will be an additional 100,000 external links to our site, although obviously they'll all be from the same (sub)domain.

If we don't seperate, our site appears to be a massive 100,000 page site, and my understanding is size is a factor in search rankings as well.

Thanks,
Paul