Kevin-

The only way you'll know if a new suspension will meet your desires subjectively is to do it, since it is a rare thing to find a sporting diesel to use for comparison. I used to own a rather highly modified 124 built at Brabus in Germany--a 'gentleman's express' kind of car. While it did not say so on their invoices, I'm willing to bet that the progressive rate lowering springs on the car were sourced from either H&R or Eibach. By the time I bought the car the previous owner had recently installed Bilstein HDs. The car ran on 16x7 modular BBS wheels with 50 series tires, which are somewhat more extreme than you are contemplating.

The car was not harsh at all. It was highly responsive and extremely satisfying to drive..almost intuitive. Its reflexes were extremely sharp without being edgy. All of this was a good thing since the engine had every Brabus mod available and was very, very strong. Small impacts were well-absorbed by the suspension and the HDs were well-matched to the springs in terms of both compression and rebound. Cornering transitions were much more secure with the performance suspension and the car could be more precisely placed in corners and rotated more easily than would otherwise be the case with stock suspension.

The only meaningful downside was the range of travel was reduced by the amount of the lowering, about 1.5 inches. Thus, on bigger hits the suspension compressed to its stops more quickly than stock suspension would, and no car handles well with infinite spring rates. On the other hand, the suspension recovered better and more quickly from the big hits and was thus easier to drive.

Subjectively, I felt the car looked much better with the suspension lowered--it was, after all, a genuine performance car and not a boulevard poser. Objectively, the modifications to the car were astonishing in terms of showcasing the performance potential built into these cars that is never appreciated in stock form. Stock, these cars offer an incredible array of virtues which can be appreciated as they are, or they can be sharpened and made more focused if the owner wishes. If you desire handling that (dare I say it?) is closer to the BMW end of the spectrum, then I highly recommend the suspension mods you're contemplating. Stick with Sportline/H&R/Eibach for springs and either Koni reds (for the fine-tuning adjustability) or Bilstein HDs. The Sports are too stiff for a daily driver, in my opinion. The sway bars are an excellent option to explore. Before you start with modifications, however, make sure that all your suspension hard and soft parts are up to spec, and make sure the car is properly aligned afterwards.

Though my family groans at the prospect, I will soon be lowering my 300SD, tastefully, in order to better match my preferences in the ride/handling/looks compromise. Enjoy your project and let us know how it turns out!

__________________
Richard Detoy
'84 300SD
'76 Moto Guzzi 850 Le Mans