I grew up playing with "Redlines" as a 7 year old in '68 and now as a big collector of the "Spectraflame" era, 1968-72, To me there all great, none are "Holy grails" and as far as appreciating, Their all equal castings in my book. Some can be easier to obtain than others due to their pricing, such as the "Olds 442", '"Bye-focal" and so on. The "Olds" would certainly be one of the most expensive redlines from that time period but I would not consider it a "Holy grail" if you had one. To me a Holy grail would be a non regular production car that is very hard to obtain... Due to the subject matter, This is only my opinion... 
