Exhaust opinion

that cam powerpeaks up near 5000rpm, but peak efficiency will be near 3500rpm. With 28" tires that will be ~28 mph with tires blazing. So you can't measure performance in first gear .
3500 in second will be ~47mph.
So what you can do is time your progress from 42 to 52 mph,in second gear, with a stopwatch.
Then repeat with open headers. You may have to rejet the carb.
Then decide if the improvement is worth the cost.
If yur still spinning at 47 mph, you don't need more power....