Joomla's and VM's capability to handle mass usage

[hofitd]

Hello,

I have a really big client who needs an ecommerce website.
I want to do it a Joomla + virtuemart based site.

I use Joomla for small websites with no massive disk and bandwidth usage , so it works great on these cases.

My concerns are that I'm not sure Joomla is capable enough to handle massive usage and http requests at the same time - this site is gonna have 1000 concurrent..
It's hard for me to believe that Joomla / VM can handle so many people at the same time.

Can you give me a list with really big websites and ecommerce websites that use Joomla and VM as it's main platforms?

Thank you so much.