30k exp/h isn't bad at L40. I maybe peaked at 40k on my mages/priest in SM:Cath, but rarely sustained that. I'd stay in Cath until 42, then move down to ZF. If you start ZF at 43-44, just do scarabs and zombies - I was able to sustain 40k+, often over 50k in ZF. Just don't start bosses until L45+