I guess I take the opposite perspective on classes; I want more classes
with fewer methods rather than few huge classes. IMO this makes for
code that easier to customize, debug, refactor and test. But true,
probably performance suffers -- especially when using class-per-file
model.
Quick response, this hasn't really been proven. I saw some stats that showed that it wasn't a huge hit. IMHO it really shouldn't make that much of a difference. It probably has more to do with OS and FS choices than per-file.