Are you guys air cooling your lights?
This has always been a typical setup for me. I've been using a 430W HPS in similar spaces for years, and in fact just got done building a new cabinet and have been doing temperature testing all week.
The space I'm working with is 2.5' x 2.5' x 7' . With an aircooled hood on its own ducting (intake and exhaust are both outside the space) the cabinet reaches a max temp of 85 deg F running the light 24 hours a day. Typical temp is 82 or so. This is door closed without any ventilation of the cabinet itself. When I dig up or replace my missing blower fan it seems like it should be trivial to knock the temp down to around 75 and keep it there--it's looking like I won't even have to run the fan constantly, which would allow me to consider CO2 enrichment.
I feel like the 400W range lights are perfect for spaces like this, but air cooling is a necessity.