As Remi had commented, this can be many factors, some well outside our visibility or control; one more to consider; outhaul/draft stability in the rig. No, it's not to deflect "blame" from fin etc, but as the speed builds up, the sail loads increase due to apparent wind loads (this can vary a little according to sailing angle, but consider you hold the same line/angle to wind) - under increased load the sail draft tends to move backwards (even in best sails - yes, but better ones move later and less) - to combat that you sheet harder with back hand - to offset backhand pull you (even unknowingly) counter by extra push on your back foot - and there comes your magic 30 kt spinout eachtime.
Typically a lot of guys use a "more powerful" negative (or non positive) outhaul in the attempt to get more power for more speed, which up to a point is correct, but the ideal sail trim for acceleration can often not be ideal for top end.
Very easy to test/try and see if this helps. You might be suprised, it's a common thing.
Cheers ~ Ian