Some weight and spring info from the Tabellenbuch:
The "first version" 230 SLs used front and rear springs with different part numbers from all the rest. "Second version" 230 SLs, and all 250 and 280 SLs use the same part number front and rear springs, and these are also the replacement springs for first version 230 SLs. The break point between first and second version 230 SLs isn't given. The compensating springs are all the same part number. Spring rates are not listed, unfortunately.
I believe the 230 SLs have a 28 mm front anti-sway bar, and the 250 and 280 SLs have a 26 mm bar.
Weights (unladen but ready to drive) are listed as follows:
230 SL
Roadster - 1295 kg
Roadster with hardtop - 1340 kg
250 and 280 SL
Roadster - 1360 kg
Roadster with hardtop - 1405 kg
Some of the weight gains, if I recall correctly, were from alterations to the body work (probably mainly the larger fuel tank in the 250 and 280 SLs, as well as some strengthening of the body). The disk brake rear axle is heavier, and the engines got progressively heavier. It's possible that the 230 SL weight is without power steering and the 250 and 280 SL weights are with power steering, but that's a guess.
Thoughts and opinions: the 230 SLs are the lightest, have a larger anti-sway bar and should have an advantage in handling over the 250 and 280 SLs; but for comparably equipped cars I'm guessing the difference is not huge. If the early 230 SL springs are stiffer, the difference might be more noticable. Comparably equipped 250 and 280 SLs should be equal.
Compare a 230 SL without power steering or other options to a 280 SL with power steering, a/c and an automatic to get the maximum weight difference, and I'll bet the difference is noticable and the 280 SL might seem "soggier" by comparison, but that's not really a fair comparison. Still, I'll bet these writers are making exactly that kind of comparison. I've also concluded over the past several years that there are damn few good automotive writers any more.
George Davis
'69 280 SL Euro manual