I have an 83 300TD and a 85 300D for my bride. Within the past three years I have owned and sold 85 300CD, 77 240D, 81 300D, and a 79 300SD. While I don't remember the wheel base and track width on any of them, the overall length of the SD was about one foot longer than the 123 cars, and the overall width was about six inches more. While the larger size makes the SD less comfortable for city driving (thats why I choose the smaller 123 cars), in my estimation the SD is by far the better car. I feel that they are all reasonably safe, but the SD has considerably more space to absorb a hit from any direction. Because the SD is heavier, combined with the extra wheel base it rides much better (smoother). The extra width and length allows the SD to handle much better. I keep my 123 cars in good mechanical condition. I have to in order for them drive half way decent. The 79 SD that I owned for a short time had so many suspension parts worn/missing (entire upper control arm bushing missing) I can't even remember the entire list, and the car still drove somewhat straight and respectable. If I so much as put tires of the wrong type (something other than "H" rating) on the 123 cars, they will suffer drivability quality. If I had any amount of open Interstate, I would choose the SD for interier space, ride, and good handling.