The additional post that i intended not to make.
a general rule of thumb for GA8, normally aspirated 2 blade prop at mtow:
600 fpm @ 5000 ft ISA
500 tpm @ 6000 ft ISA
i have had consistent 450 fpm in above config after take off at 6500+ DH in tropical mountains.
Density height charts for fixed wing are all well and good, but although they take pressure and temperature in to account they generally neglect humidity, which can be a significant factor. which is why i have quoted the above example as this was Humid (way humid) and as well as quite warm, and at 5000 elevation. airvan performed just fine at MTOW
HD