Another thought - what do you do with the car most of the time? If it's like mine, and short runs, you may want to run a heat range or two up. If it's mostly long trips, consider down. Hotter fouls less easily, but burns up quick. I'm running two heat ranges up, but my driving is mostly low speed - parades, car shows, the odd cruise night - and I can gas foul plugs if I'm not careful. (Yeah, I know - fix the jetting on the carb... but it's set up stock, and the car never really liked idling around all that well).

I think the next hotter is 46 for the Chev. 45 is general use, and 44 is cooler/long trips. Somebody correct me, please, if I remembered that backwards...

A friend with a really high miles 350 in a pickup runs the hottest range for the engine, just to keep the oil fouling from happening so fast. He's waiting to change out the valve seals - thinks that's the problem.