It was true 30 years ago, and it’s true now, that your better off with less cam than you think you need.
The Oldsmobile mentioned above had a competition cams 252 (as it was then known) which was their lowest end in terms of duration and lift.
It was perfect.
Woke the engine up without causing idle problems. Nice smooth idle, with good mid RPM performance. It might have even gotten better MPG. The Olds was my daily driver. I rebuilt the 350 with new pistons, rings, valves, valve springs, cam and lifters. The bottom end on that engine was still solid at over 100,000 miles and just got bearings. It still had the Q-jet and GM HEI ignition.
I saw so many cars at the Auto Hobby shop on base with a lumpy idle, and guys trying to get them to run right, because they had put in too much cam, too much duration. Lift was fine, but you could get more lift back then through a roller rocker kit, and skip the hassles of a long duration cam.
That weak vacuum from a long duration cam makes for brake booster problems, idling problems, and, as you note, efficiency problems. A “street/strip” cam is really just for the strip. They’re a pain to live with if you want to drive the car like a car.
Something like this would be great in your 350:
https://www.compcams.com/high-energy-206-206-hydraulic-flat-cam-sk-kit-for-pontiac-265-455.html