I recently blogged about a very large Kentico E-commerce build I was involved with at Syndicut that contained around 2 million products. Trust me, this is a major feat in itself! A lot of customisation and performance improvements were made to the Kentico build to accomodate the sheer volume of products.
A follow up post will be published soon that will detail the issues we experienced in developing a Kentico site that has to manage more products you could ever imagine and our solution to those issues.
You can have a read about the project and some of my highlights here: https://medium.com/syndicutstudio/welcome-to-our-biggest-kentico-e-commerce-build-yet-9bd2109955e0.