Captain Sim 757 was my second HD project. Oh boy, HD is madness, pure detail madness.
Thing is that in Flight Simulator X you can play with the size of the tiles, and with today Processors and GPUs you can go wild on details and they will give you an extreamly high result on the look of your sim.
So we started adding detail, handpainting everything, going from little scratches on the paint to tiny rivets or simply adding a very detailed dirt job.
So you can see here a couple fuselage paint kits that meassures 14640px wide and weights more than 1gb, can you imagine how incredibly slow an old PC can go with that amount of information?