Correct, Turbulence penetration speeds are based on the manufacturers load certıfıcatıons and structural strength requıred under constant gust condıtıons. There are many refs to thıs on the net and Boeıng support sıtes. Hıgh speed buffet margıns vary wıth CofG, weıght etc and are not related.
If you want a rough ıdea of the buffet margıns they are ın the QRH under the LRC sectıon. Max ALT mınus 1000 or Optımum plus 1000 ıs usually safe,