Avionimc, that's fairly good rule of thumb for the King Air. Tom knows his stuff!!
Another one for the B200, at least as an initial guess to what a good crz lvl is:
distance + 40 = FL. Obviosily adjusted for any local cruise rules re transition layer, really hot/heavy, significant winds etc
ie 180nm + 40 = FL220
80nm + 40 = FL120
240nm + 40 = FL280