Having three generations of vettes I find Sunoco works well in all three of the vehicles, I also find that Pioneer works well to. With the 59 I use a Medium octane and find it works very good. The 59 is a stock vehicle 283 four barrel 230 hp.The 64 I use the highest octane I can get from either company, and then sometimes I will add some booster to it. It is stock also 327/365hp (a bit more after resto.) The 75 I use medium octane, got to remember that was a low year for horse power. It has the 350/205hp. Out of the three vettes they all worked very good with the 59 and 75 using med. octane and as I said before the 64 using the highest octane. So what do you find works best for you?