Ok the title might be confusing but I do not know which would be better. I am puting a new rebuilt 350 in my work truck. The problem is I am considering doing a few mods to help performance and hopefully fuel economy. The most important question and the one that is most important is would I be better off running higher compression (64cc heads) and run 91octane or run lower compression (75cc=8.5-1) and 87 octane. I am wondering which would be cheaper in the long run more mpg and higher priced fuel or less economy and cheaper gas?