Best board in between F159 and ST115?

[Per]

Hi..
I sail my F159 with a 10.3 sail and my ST115 with 5.75 to 6.5.
Theoretically I could drop directly from the F159/10.3 to the ST115/6.5 in about 20 knots of wind, but as I prefer always to be on the smallest possible board (more fun) I think about getting a board for my 8.5 no cam freerace sail?

I´m 97 kgs and quite skilled.

Any recommendations are very appreciated. It would be nice if the extra board could work with the 6.5 for the gusty days too.

;-)
Per