Sport Today

I have been using this board since starting ws last year and am at the
stage of being able to plane, just starting to use harness, no
footstraps yet. Its specs look like this:
Length  299cm (9'10")
Wide    80cm (31.5"
Vol     190 l
Weight  11.8kg
Fin     30 - 48cm
centerboard 55cm
Sail size       4.0 to 9.6 m2

I use it on inland waters with a 6.5 sail in winds 10-20 kts

I am happy with the board and can't afford a new one anyway but would
like to upgrade from the stock 34cm fin it comes with if that is going
to make a noticeable difference. So, please, when is the right time to
upgrade? what to? and what difference will i notice when i do?

Thanks