Have not sailed a L42, so my thoughts are qualified.
Bridgedeck clearance is only one part of the "slamming equation". If other aspects are the same, the higher bridgedeck will slam less. Other considerations are the bridge deck width; a wider bridgedeck span between the hulls will slam more than a narrower span with the same clearance height. There is also bridgedeck shape; a curved and shaped bridgedeck will slam a lot less than one with large flat areas for waves to impact on.
So cats with low, wide and flat bridgedecks slam hard, whereas those with high, narrow and shaped interhull bridgedecks slam a lot less. All recent
Lagoon models can be classified as the latter.
The L42
hull shape seems very similar to our L400. These bridgedecks have no flat areas between the hulls; they are shaped, curved and moulded to include a central "nacelle". This area is also relatively narrow compared to some other
catamaran designs because of the wide hulls, and relatively high in clearance. The result is a design that does not slam as much as others of similar size.
It must be said that whilst some designs slam more and some less, it is all relative. Sailing or motoring hard into short, steep waves will be uncomfortable in all designs, but worse in some, better in others. Bearing away 20 or 30 degrees, will make all designs much easier to live with.