We a webshop with 10,000 products and and some hundred of categories in our opencart store.
When visiting any page of the site it can take up to a minute or more for the page to be loaded.
When the site contains just some hundreds of products everything loads at normal and good speed.
The website is hosted on a vps, Xeon Quad processors 2048MB RAM. This should be more than good enough
to have the site running at good speed.