When flying VFR you do not have to file a flight plan nor do you have to stick to a particular altitude except as assigned by ATC while in class B airspace. When flying below 3,000 feet AGL you do not have to fly cardinal altitudes + 500 feet either (i.e. 3,500, 4,500, 5,500, etc. ). In the scenario given, unless the ceiling rises with the terrain, you can't fly the route unless you (a) can follow valleys between the mountains while remaining VFR, or (b) file IFR.. The problem with you flight simmers is many, if not most of you don't really know anything about real flying, even enough to understand this simple situation.