The best way to evaluate the performance of a product is to try it out. To make a reasonable assessment I think it's desirable to compare the old and new side by side, if possible, in its working environment.
To check out the initial stabilizing performance difference I rocked the Adventure back and forth with both boards alternatively to see if the new board slowed the rocking moment. It did, noticeably. Looking at upwind tracking, I did a series of runs at a buoy with both boards and took a look at side slip. Again, I could tell a distinct difference.
As with the difference between the small and large rudder, I suspect the difference is likely greater at slower speeds where there is less lift and dynamic pressure available to the board.
Regarding DB flexing, I think it's a non-issue. Most boats heel (and thereby "flex" the board) magnitudes more then this board will ever bend in the water. Airplane wings flex with negligible performance differences and DBs operate on the same principle. There was certainly nothing detectable that I could note that would give the slightest inkling that this might be an issue.
I no longer race sailboats, or at least competitively -- there are many more accomplished sailors out there! But I do like to race with the Mirage Drive! In that regard, everything that makes a performance difference becomes significant and cumulative. Some of the users here will look at the DB from that perspective, and others will not.
One must distinguish between performance, aesthetics and value. The importance of aesthetics and price are different matters and highly individualistic. That said, I was a bit shocked at the price of the new board, especially compared with, lets say a new rudder. Looking at the two boards, I can't say that my old scratched and dinged board is any prettier than the new one at this point, but then I'm more likely to polish the bottom of my boat for speed than the top for looks. Accordingly, I wasted no time removing the small casting mark from the leading edge of the new board.
Personally I like the way it performs and have even grown accustomed to its humble appearance. Like skua though, I would like to see someone else review the new board, especially someone with the ability to chart track made good (or whatever it's called). Anyone in the area that would like to borrow mine for that purpose is more than welcome to do so.