We have clients running multisite with 150MM+ page views per month but on dedicated hardware and Varnish running in front of it. The latter is a must in a setup like this. You save on MRC for server rentals, which is a huge value proposition.
I run a community site that does 1m pv's a month and growing but we get hammered on 'breaking news' as wp-super-cache does not seem to handle post updates well under high use thus interested in possible solutions or alternatives.
Whereas with Varnish you're getting hot pages off RAM and on you go.
Or, you can start with this to get the general idea first: