Maximum page fetch with maximum bandwith

Question

Hi I want to create an application like a spider I've implement fetching page as the following code in multi-thread application but there is two problem

1) I want to use my maximum bandwidth to send/receive request, how should I config my request to do so (Like Download Accelerator application and the like) cause I heard the normal application will use 66% of the available bandwidth.

2) I don't know what exactly HttpWebRequest.KeepAlive do, but as its name implies I think i can create a connection to a website and without closing the connection sending another request to that web site using existing connection. does it boost performance or Im wrong ??

    public PageFetchResult Fetch()
    {
        PageFetchResult fetchResult = new PageFetchResult();
        try
        {
            HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(URLAddress);
            HttpWebResponse resp = (HttpWebResponse)req.GetResponse();
            Uri requestedURI = new Uri(URLAddress);
            Uri responseURI = resp.ResponseUri;
            string resultHTML = "";
            byte[] reqHTML = ResponseAsBytes(resp);
            if (!string.IsNullOrEmpty(FetchingEncoding))
                resultHTML = Encoding.GetEncoding(FetchingEncoding).GetString(reqHTML);
            else if (!string.IsNullOrEmpty(resp.CharacterSet))
                resultHTML = Encoding.GetEncoding(resp.CharacterSet).GetString(reqHTML);

            req.Abort();
            resp.Close();
            fetchResult.IsOK = true;
            fetchResult.ResultHTML = resultHTML;
        }
        catch (Exception ex)
        {
            fetchResult.IsOK = false;
            fetchResult.ErrorMessage = ex.Message;
        }
        return fetchResult;
    }