it seems that i have the same feeling of you when i use 4,3 in choppy conditions and over powered. I'm 90 kg and i was thinking that kode 74 was the ultimate board for 50 knots conditions. But it bounces all goes and is very hard to keep flat. It works better with 4,7 in sweeter conditions of wind and chops. I will try to put fin and straps forward as on your Acid, and perhaps the mast foot a little forward too.