Recommendation for Performance Optimization Consultancy

Can anyone recommend a consultancy group (in LA or otherwise) that can help me optimize a WAMP stack now running a D6 site?

My site at UCLA is now live in Drupal: it's not a particularly high traffic site (1000 visitors/day), and most non-cached pages are served up in a few seconds; but at peak loading (currently 100+ mostly anonymous users) non-cached pages are taking 20+ seconds to be generated... so I need some guidance in optimizing Apache, PHP and MySQL. Have trawled the forums for months on tweaking such settings during site development, but have never really been able to simulate any real load testing... until going live.

I currently have no more than 10 user accounts in the site (still really at beta), but will be opening up login more widely in a few months (potentially a few thousand user accounts), so need to get on top of this before Christmas. The module configuration is Frankenstein's monster (aren't all sites?), but I don't really want to consider culling modules just yet. Only thing that's waiting in the wings is implementing the Boost module: this will improve the anonymous user page access, but will not improve the performance of those logged in users.

I first thought about approaching 2bits.com, but they only serve Linux platforms, and I have a dedicated Windows 2003 server (2bits seem pretty explicit about not 'doing' M$ servers)... so is there anyone else out there that people can recommend?