Lost City of Gaxmoor was playtested with an old school-type PC group of 8 or more 1st level PCs, I remember EGG said, and assumes several PC deaths per encounter in the early bits (all EL4-6+). For a more standard 4-PC, few-deaths game I'd recommend it for level 5 at the start, maybe a strong 4th. Encounters go up to EL 20+; with one CR 20 villain my PC group still hasn't defeated after nearly 2 years...