What is the best memory buffer size to allocate to download a file from Internet?

Question

What is the best memory buffer size to allocate to download a file from Internet? Some of the samples said that it should be 1K. Well, I need to know in general why is it? And also what's the difference if we download a small .PNG or a large .AVI?

Stream remoteStream;
Stream localStream;
WebResponse response;

try
{
    response = request.EndGetResponse(result);

    if (response == null)
        return;

    remoteStream = response.GetResponseStream();

    var localFile = Path.Combine(FileManager.GetFolderContent(), TaskResult.ContentItem.FileName);
    localStream = File.Create(localFile);

    var buffer = new byte[1024];
    int bytesRead;

    do
    {
        bytesRead = remoteStream.Read(buffer, 0, buffer.Length);
        localStream.Write(buffer, 0, bytesRead);
        BytesProcessed += bytesRead;
    } while (bytesRead > 0);
}

Answer 1

For what it's worth, I tested reading a 1484 KB text file using progressive powers of two (sizes of 2,4,8,16...). I printed out to the console window the number of milliseconds required to read each one. Much past 8192 it didn't seem like much of a difference. Here are the results on my Windows 7 64 bit machine.

2^1 = 2 :264.0151
2^2 = 4 :193.011
2^3 = 8 :175.01
2^4 = 16 :153.0088
2^5 = 32 :139.0079
2^6 = 64 :134.0077
2^7 = 128 :132.0075
2^8 = 256 :130.0075
2^9 = 512 :133.0076
2^10 = 1024 :133.0076
2^11 = 2048 :90.0051
2^12 = 4096 :69.0039
2^13 = 8192 :60.0035
2^14 = 16384 :56.0032
2^15 = 32768 :53.003
2^16 = 65536 :53.003
2^17 = 131072 :52.003
2^18 = 262144 :53.003
2^19 = 524288 :54.0031
2^20 = 1048576 :55.0031
2^21 = 2097152 :54.0031
2^22 = 4194304 :54.0031
2^23 = 8388608 :54.003
2^24 = 16777216 :55.0032