As said before and repeating again, It is always much easier to tune and increase a too small or "cheap" rig than a bad hull and keel. So, since I think the Oceanis 38 is such a good looking boat, both externally and especially internally, it is nice to read that the basics seems in place and adequately designed for good performance.
I personally would rather buy the Oceanis 38 and fix the rig instead of buying the comparatively traditionally designed Dehler with its missing hull windows. Or let's say it like this, do not show the Oceanis interior to your wife if you prefer another boat
On the other hand, a Dehler 38 with the Oceanis modern interior and hull windows and a super interesting package for our taste would be created. Partly it is already on the market but far too expensive. I am talking about the Solaris One 37.
Anders, the Solaris 37 has not the same type of hull of the Oceanis 38 but the type of hull of a Salona 38 or XP 38. Both have a far superior sailing performance regarding the Solaris 37. The Solaris 37 has a good sailing performance (better than the Oceanis 38, specially upwind) and a very good quality interior. A delightful boat, I agree, but not with a versatile interior like the Oceanis.
Regarding increasing performance on a hull like the Oceanis 38 I had already talked about this with you and that's when I talked about the boat needing to have a bigger B/D ratio for that.
As you know the boat has a smallish rig and to increase performance you would have to put a bigger rig, but rigs on sailboats are calculated regarding RM of the boat and knowing Conq taste for fast boats I am sure that boat has a rig as big as it can have with the present design parameters. To put a bigger rig it would be necessary to increase ballast and for that all boat structure would have to be reinforced resulting in a much more expensive boat. Not a thing one can do on a standard boat with Beneteau.
I agree the boat has a great interior and as test sailors have showed that boat has a very good performance downwind with lots of wind, were ballast is not as important and the big hull form stability and hull design give it an advantage.
Upwind, specially with waves, the boat would be very far away from a Dehler 38 simply because it has not the power to go against them with speed and overcome its superior wave drag. It is upwind that the ballast counts most compared with hull form stability.
I am not saying that the boat is not suited for you, it is a great sailboat regarding what is designed for, but not a performance cruisers. You are used to sail faster than other cruisers on the Opium 39. With this one with light conditions or upwind you will not have such look and all performance cruisers will be faster as well as some modern mass production cruisers of the same size.
That would have no importance to many but it causes me some confusion you consider downgrading performance from the Opium 39 to the Oceanis 38. I would have hated it. Yes the Oceanis 38 has a nicer and bigger interior than the Opium 39 and I understand that your wife would much prefer it but do you prefer it?
Anders since you are interested in the Oceanis 38 can't you ask to Benetau a Polar speed or speed chart just to see what is its performance? Benetau hates to give that sort of stuff even if Finot/Conq has it, but if you insist I am sure they will provide you with one.