Rx.NET - Concurrency test

void Main()
{
    var urls = new[]{ "url1", "url2", "url3", "url4" };
    DownloadFiles(2,urls).Subscribe();
    Thread.Sleep(5000); // delay program quitting to observe threads output
}

public class DownloadResult { /*...*/ }

public Task<DownloadResult> DownloadFileAsync(string path)
{
    return new Task<DownloadResult>(()=>
    {
        ("Started : " + path).Dump();
        Thread.Sleep(1000); // the download activity (i.e sync method) ... WebClient.DownloadFile
        ("Finished : " + path).Dump();
        return new DownloadResult();
    });
}


public IObservable<DownloadResult> DownloadFiles(int maxConcurrent, string[] paths)
{
    return paths
        .Select(path => Observable.FromAsync(() => DownloadFileAsync(path)))
        .Merge(maxConcurrent: maxConcurrent);
}