My LANG 36" RF only takes about 20-30 minutes to get to 300. I've not noticed any problem with the rack heating up higher than the rest of the chamber as it sits several inches above the plates.
The area closest to the firebox gets a bit hotter than further away, but not significantly.
I LOVE my LANG!!!
CMJ - KCBS
CBJ - MBN, NCBS, NCPC
OBJ - BBQCritic.com
CTC - KCBS
Pitmaster and chef - "4 Lil' Pigs" Competition BBQ Team
Author of "A 'Q' Review"
Lang Hybrid Smoker, BDS, Holland "Epic"