Hello
I can only comment regarding Kentico CMS really as I have been using it for a long time and in my experience Kentico can handle your requirements perfectly!
The user experience is amazing and always improving. Kentico’s latest version (version 8.1) is far smoother and easy to use than ever before. With my experience with them, Kentico listen to us and want to always improve, so suggestions are always welcomed and improvements are applied :).
With such situations like yours, it would be good to contact Kentico as they are always happy to help and provides suggestions on how to handle large data sizes. http://www.kentico.com/Support/Consulting/Overview
So I would heavily recommend Kentico to you. They also have an awesome Kentico EMS version, which enables Online Marketers within your company to utilise the CMS for lots of Online Marketing such as A/B Testing, MVT Testing, Content Personalisation and Marketing Automation to just name a few of the features!
You could always download a demo of Kentico to see how you like it? http://www.kentico.com/Download-Demo
Thanks
Ilesh Mistry
Solutions Architect at MMT Digital and Kentico MVP
