Topic: Benchmarking or profiling dev environment load

We are hitting around 500+ modules and classes and the development environments have slowed down significantly (possibly more since moving to rails3).  Adding certain models and lib directories to the load once paths helps, but has it's obvious drawbacks.  I'd like to see if I can get benchmarks at a module/class level, to see if we could maybe pick and choose which to refactor or move into a load once path.  Has anybody had any success benchmarking this kind of thing with Ruby-prof or some other tools?  I can't get the right output out of ruby-prof.