StringBehavior.cs

public class Program
{
    static void Main()
    {
        BenchmarkRunner.Run<Harness>();
    }
}

public class Harness
{
    private static readonly string a = "1d76e414-21b4-49f8-855d-6c0bb76aa210";
    private static readonly string b = "6e38457f-4d8c-4056-8a64-a42fcd78127a";
    private static readonly string c = "8a8a6c5c-dee6-4407-b146-fb870736b860";
    private static readonly string d = "e391da11-c962-42f0-ab48-5c7fe8001abd";
    private static readonly string e = "040a44d4-fb1f-43d2-8bbc-4b6de42405b3";

    [Benchmark(Baseline = true)]
    public string Plus() => a + b + c + d + e;

    [Benchmark]
    public string Concat() => string.Concat(a, b, c, d, e);

    [Benchmark]
    public string Interpolate() => $"{a}{b}{c}{d}{e}";

    [Benchmark]
    public string InterpolatePlus() => $"{$"{a}{b}{c}"}{d}{e}";

    [Benchmark]
    public string InterpolatePlus2()
    {
        var x = $"{a}{b}{c}";
        return $"{x}{d}{e}";
    }

    [Benchmark]
    public string StringBuilder()
    {
        var sb = new StringBuilder();
        sb.Append(new[] { a, b, c, d, e });
        return sb.ToString();
    }
}