high traffic

We operate a personals site with 150K+ members. The current backend is a custom-developed PHP / MySQL application that is not fit for our needs in terms of stability, performance and ability to add additional features. Budget $10k+

We are looking for an experienced Developer who is an expert in PHP, MySQL and Drupal to
(1) Duplicate the feature set of our existing site using Drupal
(2) Write custom modules for features that don't exist in the Drupal Core or a stable add-on module.
(3) Write a custom migration script to port member data and photos from old database

Here is my initial post about performance tuning our site http://www.divx.com/ This is mainly a place for me to brain dump and spark discussion and hopefully open up issues to track and get some of these fixes into Drupal core.

Servers

4 - Web servers with 8GB Memory each, Apache 2.2.x + PHP 5.2.x
2 - Memcache Servers with 8 GB Memory each. 9 bins per server
2 - Database Servers with 16GB each running MySQL 5.0.x

Traffic