I've tried to go through the groups and forums to glean as much information as I could prior to posting this. I fall into the category of someone who is fairly familiar with drupal and mildly familiar with server setups. There is a wealth information on Performance and tuning, but it leaves the novice without a clear path of how to scale. I though I would post my setup here along with my confusion, in hopes that it will help other individuals in the same boat.
My Current Setup
I currently have 400K nodes and 100 users
I hope to be able to scale to 100k + users 5M Nodes
I'm using Domain Access for different "affiliates" (over multisite because some data needs to be shared across sites)**
I am currently using drupal 6.2 on Media Temple (have read that virtuoso really slows things down)
I have somewhere in the neighborhood of 60 modules enabled
I expect a 30% / 70% ratio of authenticated to anonymous users
**not sure how this will effect performance, originally contemplated using multisite to split up the number of nodes for performance. Domain access lets you change table prefix per domain, whiich I think may help performance some.
Path To Scale?
Boost and Memcache
Memcach and Varnish
Pressflow? (im a confused if pressflow is just drupal with some code mods, with these modules pre-configured or something different)
Pantheon ? (im also confused about the difference between Pantheon and Murcury ... is pantheon a service or a tuned customized version of drupal)
Migration to Rackspace - (deploy files on CDN and be able to create a new "instance" on demand
Add load balance / separate DB server
Some Resources
Drupal Documentation On Performance: http://drupal.org/node/627252
Rackspace / Drupal on the cloud http://www.rackspace.com/cloud/blog/2010/05/25/deploying-drupal-in-the-c...
Optimizing Drupla on Rackspace http://www.rackspace.com/cloud/blog/2010/02/02/optimizing-your-drupal-si...
Patheon http://getpantheon.com
Also, I'm leaning toward rackspace just because it seems like the feedback has been a tiny bit better, the Amazon setup seems equally feasible (although maybe a tad more complicated)
Thanks allot in advance