[JohnRPollard]

Speaking as someone that has considered both these boats, here's my take:

The 400 appears to be a more evolved hull form. I do not doubt that it will out sail the 42, and likely has every bit as much interior volume (maybe more).

To my mind, the distinguishing factor comes down to whether you are interested in a two-cabin boat or a three-cabin boat.

Both boats offer a choice. But if you get a 3-cabin 400, the "owner's" cabin gets split into two smaller cabins. This leaves no larger-sized owner's cabin. Essentially the guest v-berth becomes the "owner's" cabin.

Whereas if you get a 3-cabin 42, the "owner's" cabin (whether pullman or centerline) is retained and a third guest cabin is added at the port quarter (in lieu of storage lockers).

Regardless of differences in hull design, helms, etc, if I wanted a 2-cabin boat, I'd take the 400. If I wanted a 3-cabin boat, I'd take the 42.