When you say '25 knots plus', I am assuming that means 25 knots and a little over???
'Speed Sailing' is really only starting at that wind speed. For many of us, "Speed Sailing' starts at 30 knots plus winds and 40 knots of speed,

and that a quite a different kettle of fish. For me at 72 Kg, that means my 40cm wide, 60L Carbon Art speed board. Even in just over 25 knots wind, it is faster on a speed run than any of my small slalom boards.
But of you also want to do Alphas and 1Hr's etc, then you will be better off on a small slalom or
large speed board.
For that sort of sailing, at 25+, unless you sail in a spot with very fluky winds, you should be looking at narrower boards from 55cm down to 50cm and roughly 10-15 litres under your body weight (but Litres is the least important factor - width. length and rocker shape are much more important).
Fins are also important. Not so much the brand, but the style of fin to suit your purpose and conditions, and the size. They are often dictated by the conditions you sail in. Weed fins for ...well... weed! Short, wide, Delta type fins for shallows etc. Smaller is faster off the wind, but sometimes less forgiving. Larger is faster beam reaching and upwind but can be a control handful downwind at high speed. Assy is definitely faster on good speed courses but don't get an Assy that is made specifically for a canal where they ferry you back upwind on a trailer!

Better are the less extreme Assy fins designed to work on the upwind as well - (Time machine, KA and Tribal Assys all get you back upwind well).
Everything is a compromise. If you seek your ultimate speeds, less compromise helps speed but makes equipment choice and skills more vital.
And best speed is made but a really balanced combination of Board fin and sail for the rider in the prevailing conditions.
More board width is not faster in choppy conditions. More
control is. For many, that may be a wider board they are more comfortable on, but ultimately, narrower boards of suitable design are faster.
Have a browse of the posts of fast sailors of your weight and similar general sailing conditions and see what they are using successfully.