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?
I am not writing this because I necessary is contemplating to "downgrade" to the Oceanis, this is more a general discussion continuing from the debate we had earlier regarding Oceanis 38 and B/D-ratio.
I do not think we need to repeat the discussion earlier but remeber the facts I gave about this boat, other similar boats and the Oceanis 40 I owned before. Based on that I still think the Oceanis 38 can carry a bigger rig. The swedish EYOTY-jury memeber testing the boat the same day as I did, totally agreed with me on that and said that Beneteau should do a Jeanneau and offer a performance version with bigger rig.The magazines testing it for the EYOTY now during the autumn seems to think it is a very good performer in higher winds. Should not be that if B/D-ratio would be totally off.
Since I have owned a tweaked Oceanis 40 for 3 years I know pretty well how a boat like this compare to a similar sized performance cruiser and I maintain that to use words as "much slower" or "not at all comparable" is not true. A well sailed boat like this, with good sails and rig components, can stand up very well to boats like Salona 38, Dehler 39 etc in normal family sailing. But not beating into 22 knots of wind in a competition, with mainsails without reefs, for example.
But, as I wrote before, my Oceanis 40 is, among all the boats I have owned over the years, one of the best boats beating into choppy seas if wind is pretty stable so the single rudder is not ower pressed. It was also one of the least noisy inside.
Even if we have minor speed differences between boats mentioned here, I do noth think they are so big that they necessary in all cases have to stand above other aspects in choosing a boat. Of bigger importance I think is the lousy equipment manufacturers keep throwing at the family cruisers. Replace that and you might have a pretty decent boat at a still very good price.