Mechatronics in Germany do some great performance work on our W113 cars. Do a search on this forum and other internet web sites to learn more about Mechatronics. In addition John Olson here in the USA make performance suspension kits.
If money was no object and wanted both performance while keeping the classic Pagoda looks, I would go with Mechatronics. You probably can work with Mechatronics to get the kind of performance ( maybe even a 5 or 6 speed mated to an AMG motor) and luxury (maybe electric windows and electric canvas top mechanisms) that you desire.
Myself with limited funds, I went with John Olson springs, 15" Bundt rims, and better performing 15" tires (to get rid of the roll around curves/turns and the front end dipping during stops). My normal mechanic would not install this modification because it was not standard/original; so I had another mechanic do it; along with new kingpins and suspension bushings. Nevertheless, when my normal mechanic did drive the car with the modifications later on, he said it was one of the best driving and handling W113 he has even driven. My normal mechanic did install a Nardi steering wheel and a Nardi shift knob which I like for a more sporting look and feel.
Good luck in your endeavors.
Danny
1970 280SL Euro silver 4-speed