E-Commerce WordPress Performance Concerns

Hello,

I’m in the planning stage of an e-commerce (and more) website and I’m considering using WordPress along with WP.osC, ShopperPress, or PHPurchase. My concern is that the site may eventually become so large that page load and overall site response times might become an issue. Initially, in addition to Home, About, Contact, and Blog pages, the site will have multiple Product pages displaying 100-150 different products in different categories for sale, but the site could grow to 1,000 products over time. The site will also have some Flash animation, along with membership and affiliate plug-ins. Has anyone built a site of this size before using WordPress, and if so, how have response times been? What other kinds of problems might I encounter using WordPress for a site like this?