My ten cents. I live for torque. I've had two 6.9s and multiple 300D's, concluding with a '97 E300Turbodiesel (Euro). Two different worlds. The later CDI diesels are probably superior to a 6.9 in terms of numbers but not aural pleasure. The 300D as a five, then six, then turbo was great but nothing like a 6.9. If you've driven a 6.9 that is sorted, good suspension, good oversize tyres, IT'S SO MUCH FUN! for a 70's taxi/limo. I blew my tranny to bits and ended up buying a donor car which I still have.
I had some serious fun with my E300Turbodiesel. I had it chipped and dyno tested to 210bhp (DIN). Great for doughnuts. Sold it to a taxi driver about five years ago. Still going. Never told him it was chipped.
With both my 6.9's I fitted new OEM spark plug lead sets. Both cars transformed for $80 each.

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'66 W100 600 SWB
'05 W463 G55K AMG
'91 W126 500SEL
'93 W463 300GDL
'84 W460 280GES
'83 W460 300GDL
'66 W111 220SEb Coupe
'58 W121 190
'58 W180 220S
Have previously owned '99 SL600, '99 ML320, '79 450SLC, '79 450SEL 6.9 x 2, '68 600, '91 190E 1.8, '90 190E 2.0, '85 190, '90 500SL, '92 500SEL, '97 E300Turbodiesel, '91 300D, '72 280S, '82 300D, '81 300SD, '85 230E, '56 220a and I'm sure I'm forgetting some.