Poorly programed maps WILL cause lag. Especially any map that has vehicles. It is not even a matter of cpu usage as much as an issue of the limitations of the engine itself. Think of the server as a race track that lets cars go 200mph the problem is that the srcd can only go 150mph before it blows up. At the end of the day a problem in the programing of the game or the engine of a car can not be overcome by the quality of the road.