A lot depends on cam selection if you decide to go with either of those setups. If it is going to be primarily a street car with some highway driving, you are probably going to want a mid range cam with a power band that starts lower. The reason I say this is because you are focusing more on the highway driving end and do not seem to be considering the city/town driving conditions that may predominate your driving. When you are in town where the speed limit is 30 mph with the 3.31 you will be chugging along at about 1600 rpms in 3rd gear (unless you want to be cruising around in 2nd). With the 3.54 you will be running at 1750 rpms. Most aggressive cams do not like to run below 2,000 rpms and their longevity may be compromised by inadequate
oil flow at low rpms.
I would suggest a more moderate cam and the 3.54. I had a 3.54 in my ERA with a 428 pushing about the same horsepower and a 4 speed wide ratio top loader. Thought that it was a good setup for being able to have enough power to go around town at 30-35mph and not stress the engine.