I have the 520d, the car is that well insulated that there is no vibration. You save a shed load of cash over 3 years by going for the smaller engine, and like you say get to choose some comfort options. If you're happy with the performance of the s80 then I'd say it's a no brainer.
If budget was no option i'd get a 535d but how many of us are lucky enough to be in that position? Also consider the comfort seats