Yes. it has been quite a while.
I'd say your thinking on these 2 boards is pretty good, but I wonder why you are getting two boards so close to each other?
The volume (125 ltr vs 115 ltr) and the width (69cm vs 65 cm) are quite close so I'm not sure you are going to get the difference in ride through the chop you seem to want/need.
This would seem especially true since they are both the same design.
Why not go down to a smaller board (100-110 liters) and about 60-62 cm wide?
Sailors can normally use a 7.5 m2 rig on a 100 liter board without much problem.
As far as the fin size goes, you will be able to use your 46 cm on the 115 Tabou
for really marginal conditions, but you may find the 37/38 works better.
A larger fin can help you get on plane, and maybe a little to stay on plane in the
holes, but it will not help with the chop and that seems to be the reason you are
looking at a smaller board.
Hope this helps,