I'm not familiar with the SM, but the main differences with the 'S' model are:

The 'S' Model has a rear subframe, the 'E' does not
The 'E' Model has a different Carb, Cams and a higher compression ratio (not good for that 'SPECIAL' petrol you get from African stations, but still MILES better than a KTM)
The 'S' Model has a cooling fan, the 'E' model does not.

The last point is the most relevant for those of us prepping bikes because an 'S' model tank will almost always fit on an 'E', but 'E' model tanks, particularly older ones don't fit on 'S' models because the tank often takes the space required for the cooling fan on the right radiator.

For those prepping an 'E' model and worrying about overheating without a fan, you can obviously retro fit one from an 'S' with a manual on/off switch, which you can operate based on the engine temp (get an oil dipstick temp gauge), or you can get a 1.6 bar radiator cap to replace the standard 1.1 Bar item (make sure you check the quality of your radiator hoses before running this) and run a product like 'Water Wetter'. In direct tests in soft desert sand between two DRZ's the bike without a fan running water wetter ran 20 degrees cooler than the standard antifreeze/fan equipped 'S' bike and never boiled over approx 20000 desert Km.