Author here: Yeah, I was surprised that there doesn't seem to be many options for extra optimizations in the Go compiler. Would be curious if Go experts have more insight or other compiler recommendations.
GOGC=-1
EDIT: Trying it out quickly shows a small improvement actually, but so small as to likely be noise as I was doing other things on the machine. Summary
./mainnogc 1000 ran
1.01 ± 0.06 times faster than ./maingc 1000