If by high tensile you mean the 10.9 or 12.9 grades then no. There's no point using a fastener of a higher strength than needed to generate the required clamping loads and high tensile bolts are more brittle than lower tensile ones which gets even worse after the heat cycling at such high temperatures. In the end the heat cycling removes the extra strength of the high tensile bolt and leaves it weaker and more brittle than a lower tensile one would be. What you need is a ductile material in high temperature applications and short of using special steels a grade 8.8 stud or bolt, fitted with antiseize such as Copaslip will do the job fine.
Brass nuts used to be a favourite on old British engines because they don't corrode onto the stud.
