Ran some becnhmarks on the following code.

concat_test.go

package concat_test

import (
	"fmt"
	"strconv"
	"strings"
	"testing"
)

var ipAddr string = "127.0.0.1"
var PORT string = "8080"
var port int = 8080

func BenchmarkConcatStrconv(b *testing.B) {
	for i := 0; i < b.N; i++ {
		fmt.Sprintf("http://" + ipAddr + ":" + strconv.Itoa(port) + "/v1/api/1")
	}
}
func BenchmarkConcat(b *testing.B) {
	for i := 0; i < b.N; i++ {
		// assuming port is a string here
		fmt.Sprintf("http://" + ipAddr + ":" + PORT + "/v1/api/1")
	}
}
func BenchmarkSprintFDigit(b *testing.B) {
	for i := 0; i < b.N; i++ {
		fmt.Sprintf(fmt.Sprintf("http://%s:%d/api/1", ipAddr, port))
	}
}
func BenchmarkSprintF(b *testing.B) {
	for i := 0; i < b.N; i++ {
		fmt.Sprintf(fmt.Sprintf("http://%s:%s/api/1", ipAddr, PORT))
	}
}
func BenchmarkStringsJoin(b *testing.B) {
	for i := 0; i < b.N; i++ {
		fmt.Sprintf(strings.Join([]string{"http://", ipAddr, ":", PORT, "/v1/api/1"}, ""))
	}
}
func BenchmarkStringsJoinStrconv(b *testing.B) {
	for i := 0; i < b.N; i++ {
		fmt.Sprintf(strings.Join([]string{"http://", ipAddr, ":", strconv.Itoa(port), "/v1/api/1"}, ""))
	}
}

results.md

OS X 10.8

#Results

Go 1.0.3

go test -v . -bench=".*"
testing: warning: no tests to run
PASS
enchmarkConcatStrconv   5000000	       611 ns/op
BenchmarkConcat	 5000000	       474 ns/op
BenchmarkSprintFDigit	 1000000	      1010 ns/op
BenchmarkSprintF	 1000000	      1057 ns/op
BenchmarkStringsJoin	 5000000	       654 ns/op
BenchmarkStringsJoinStrconv	 2000000	       789 ns/op

Go 1.1beta2

go test -v . -bench=".*"
testing: warning: no tests to run
PASS
BenchmarkConcatStrconv   5000000	       491 ns/op
BenchmarkConcat	 5000000	       395 ns/op
BenchmarkSprintFDigit	 5000000	       667 ns/op
BenchmarkSprintF	 5000000	       668 ns/op
BenchmarkStringsJoin	 5000000	       524 ns/op
BenchmarkStringsJoinStrconv	 5000000	       616 ns/op