Dont touch a gazelle, they are very expensive to maintain, Turbomeca no longer supports the engine. Last engine overhaul about £ 150k for 1700 hour life. Drinks fuel like its going out of fashion. Unless it is a stretched one back seats worse than a 500 in terms of legroom. One I fly for a customer just spent months and months and about £37 for a new clutch.
Incidentally dont expect to put 5 people and a full tank in a 206 and get it off the ground !!
SASless how do you work out the 500 burns more fuel ? Both have a C20B engine unless the 500 has had a C20R retrofitted. Having had both, at 100% 206 about 110 - 120 ltrs /hr an hour 110 kt cruise. 500D 75 psi 130 plus again 110 ltrs an hour so 500 will use less fuel by nearly 20% on any journey.