I have both, w111 coupe (six cylinder) and w113, you are right the ride that you get on a w111 is much more comfortable than w113 but don't forget w113 is a sports car versus a touring car the sl is a lot rougher ride mostly due to shorter wheel base. I really don't think you can compare the two, at the time of production the coupes cost almost twice as much as Sl's so that tells me that w111 were meant to be a luxury car and the evidence is very clear, interior is all leather, lot more wood & much more.
Mechanically, with the exception of the engines they are very similar, engine of a 3.5 is a bit more complicated than the six cylinder, I would say if you were able to manage taking care of a 3.5 a w113 will be somewhat easier.
Finally, there is nothing like driving a beautiful convertable on a nice day, especially in a nice warm climate like Dubai.
Hope this helps!