Interresting thread !
I had the opportinity to make my own opinion, having played with the suspension and wheels of my former 1.4 petrol and my current 1.6 FSI.
But what I've found is very different. That's for my driving style, of course, although I'm also relatively concerned about comfort.
My "CV" follows...
1.4 petrol w/OSS : with std suspension + 15" wheels, then with 17" wheels, then FSD/Weitec -30/00 + 17" wheels, and finally with FSI front springs and 16" wheels.
1.6 FSI w/OSS : with std suspension + 16" wheels, then FSD/Weitec -30/00 (front springs for 1.4 !) + 17" wheels, then FSD/ std front 1.4 springs (doh! stupid me) + 17" wheels, same with Whiteline rear ARB, finally with genuime S-line springs for FSI w/OSS, FSD's, rear ARB + 17" wheels. And the same setups but with winter tyres on 15" wheels instead.
My nr1 conclusion is that the factor that has the biggest impact on comfort is the wheel diameter. Well, in fact, it's the tyre profile, but we cannot play alot with it. Moreover, bigger wheels are most of the time (much) heavier, so they degrade acceleration and braking too. Too bad 17"'s look so good
I've driven a long time with my FSI on too soft springs, and it was awful ! Way too much body roll, and bottoming up.
That said, an TDI is even slightly heavier than an FSI...
As many others have also found, my opinion is that the better compromise on handling vs. comfort is obtained with 16" wheels.
I found an improvement with FSD shocks aswell.
Now I have the "elk" stance with the S-line springs on the 4 corners, because of the FSD's, but at least the car handles correctly. What a relief !
Maybe a solution would be spacers to slightly raise the rear ?