Yes, one mans opinion, but if you are going to spend the money to build a 408, wouldn`t you want to tune it to get the most from it ?. That just can`t happen when using 87 octane gas, but what ever works for you.

 

A 408 build won't cost much more than a stock 5.9 build, when properly shopping for parts. Sure, I could certainly make more power building for higher octane, but that's not my goal or purpose for this motor.

 

I use ethanol free 91 octane. I don't think we have 93 here.

 

94 Chevron here. I do my best to stick to one gas station not a mom and pop one either. If the fuel has lead in it, it will foul the 02's and kill the cat.

 

I use 91-92 with the Hemifever SCT tune.
Yup, it costs a bit more to fill the tank, but I get at least one extra day (~60 miles) out of a tank, so the net cost increase (if any) isn't much at all.
Now, if I'm a good boy and keep my foot out of it (drive real mellow), I'm just in front of where I was with the 87 tune... but, if I need a little get up and go for any reason, it is available right under my foot.

It's a matter of setup, driving habits, and yes, personal preference.

My wife's Dart (1.4T) is supposed to use 91+ by the book... there are many on the Dart board the refuse to us it and only fill up with 87... they all complain about not getting close to the spec'd mpg.
Yup, the Dart cost more to fill than the Neon, but it gets a half week more out of a tank... net cost is down, and it goes a heap faster.

I guess you can see where our preference is