38 total seem a bit much. I'v always had luck with 35 total.

How much do you drive it? Around here, there's a handful of places that sell 100 octane unleaded at the pump for $7.25 a gallon. One place is even open 24hours. You could put a 1/4 tank of that and top off with pump premium. I run straight 100 unleaded, but I have almost 13 to 1. My car loves the stuff!

For longer road trips, I plan on fitting a small 10 or 15 gallon fuel cell filled with leaded 110 that's plumbed to be partially drained into my custom main tank.

I figure I can add 5 gallons of the good stuff just before I fill up with premium unleaded and with the fuel cell, be able to mix up 2 or 3 batches of decent fuel out on the road.