I bought an Arcadia 2 x 250W MH DE HQI. It is less than 4" high has no fans and internal ballasts. Its worked great for the pst 6 months and I don't think Arcadia would put their name on it if they didn't think it would have satisfactory cooling. Although expensive I ebayed mine for a great price. Hikari is the north american distributor, however I don't know who retails them. It could be worth a look. Mine is the series 3 pendant
http://www.arcadia-uk.info/