The bottom line is: the time necessary to optimize Ruby to run below 8 minutes was bigger than he could afford, and apparently Go, once written (which apparently gave the OP some issues) needn't be optimized.

That said, Go wasn't necessarily the better choice, because of the subtlety that made the Go program overflow silently. Writing the solution in Scala or even in JS would have probably given him less of an issue.

It's not.