i have had an engine with an arp stud and nut running aprox 350 bhp, it was spot on .
However my new one has long studs, but people will tell you different things, some say standard head bolts will handle 500 some say it wont.
Personaly at 450 i would be long studding, and i aint a fan of only doing 6, as i would see a weak point on the outer studs. Just my oppinion long stud the lot and do it properly just the once .