StringBuilder vs. String.Concat (2)

open System
open System.Text

type Thing() = class
    member val Name = "Something" with get
    override this.ToString() = this.Name
end

let random, sb, n, thing =
    new Random(),
    new StringBuilder(),
    100,
    new Thing()

#time "on"

for i = 1 to n do
    String.Concat(thing.ToString(), thing.ToString(), thing.ToString(), thing.ToString(), thing.ToString())
    |> ignore

#time "on"

for i = 1 to n do
    sb.Length <- 0
    sb.Append(thing.ToString()).Append(thing.ToString()).Append(thing.ToString()).Append(thing.ToString()).ToString()
    |> ignore
;;

/*
ITERATIONS: 100
    --> CONCAT
    Real: 00:00:00.000, CPU: 00:00:00.000, GC gen0: 0, gen1: 0, gen2: 0
    val it : unit = ()

    --> STRINGBUILDER
    Real: 00:00:00.000, CPU: 00:00:00.000, GC gen0: 0, gen1: 0, gen2: 0
    val it : unit = ()

ITERATIONS: 1000
    --> CONCAT
    Real: 00:00:00.000, CPU: 00:00:00.000, GC gen0: 0, gen1: 0, gen2: 0
    val it : unit = ()

    --> STRINGBUILDER
    Real: 00:00:00.000, CPU: 00:00:00.000, GC gen0: 0, gen1: 0, gen2: 0
    val it : unit = ()

ITERATIONS: 100'000
    --> CONCAT
    Real: 00:00:00.057, CPU: 00:00:00.062, GC gen0: 6, gen1: 3, gen2: 1
    val it : unit = ()

    --> STRINGBUILDER
    Real: 00:00:00.009, CPU: 00:00:00.015, GC gen0: 2, gen1: 0, gen2: 0
    val it : unit = ()

ITERATIONS: 1'000'000
    --> CONCAT
    Real: 00:00:00.142, CPU: 00:00:00.156, GC gen0: 63, gen1: 3, gen2: 1
    val it : unit = ()

    --> STRINGBUILDER
    Real: 00:00:00.064, CPU: 00:00:00.062, GC gen0: 24, gen1: 0, gen2: 0
    val it : unit = ()

ITERATIONS: 100'000'000
    --> CONCAT
    Real: 00:00:09.612, CPU: 00:00:09.609, GC gen0: 6294, gen1: 3, gen2: 1
    val it : unit = ()

    --> STRINGBUILDER - 30% FASTER
    Real: 00:00:06.321, CPU: 00:00:06.318, GC gen0: 2479, gen1: 1, gen2: 0
    val it : unit = ()
*/