Thanks for all the advice so far.
Looks like I'll be planning 3 routes then: over the top, to the east, and to the west.
Another question if I may; how much clearance over the mountains would be enough on a normal day to keep the passengers comfortable? Will a couple of thousand feet give clearer air, or are we talking tens of thousands?
Still undecided over the plan - especially as 'over the top' seems unlikely.