Without using SmartWebResources, you could try using IIS 7 compression, here are some article regarding IIS 7 compression, Configuring HTTP Compression in IIS 7 and Getting IIS 7 to Compress JavaScript

If you wish to do it in the client side, my suggestion is to use the WebGrid initialize event handler to set the row position property of each row to the RowNumber cell. Here is the snippet for such scenario, in this case the RownNumber cell is the first column in the WebGrid:

function WebGrid1_OnInitialize() {
    var grid = ISGetObject("WebGrid1");

    var rows = grid.RootTable.GetElement(WG40.BODY, WG40.HTMLTABLE).getElementsByTagName("tr");
    
    for (var i = 0; i < rows.length; i++) {

        rows[i].getElementsByTagName("td")[1].innerText = grid.GetRowByElement(rows[i]).Position + 1;
    }
}

On the other hand, the method will be similar for server side as well, however you will need to use the InitializeRow event handler:

protected void WebGrid1_InitializeRow(object sender, ISNet.WebUI.WebGrid.RowEventArgs e)
{
    if (e.Row.Type == ISNet.WebUI.WebGrid.RowType.Record)
    {
        e.Row.Cells[0].Value = e.Row.Position + 1;
        e.Row.Cells[0].Text = (e.Row.Position + 1).ToString();
    }
}

We have an article regarding client footprint optimization in our blog in the article Rich Feature in Low Client Footprint. The article discuss the ways to reduce the client footprint.

A sample for such scenario has been provided in the WebCombo sample LoadOnDemand.aspx. An article in the WebCombo documentation has also been provided for LoadOnDemand in the article titled "Load On Demand" and "How-to: Apply load on demand in WebCombo"

You could also utilize Load On Demand for self reference and paging in order to let the WebGrid load less data initially. The self reference load on demand sample has been provided in WebGrid tutorial SelfReference_LoadOnDemand.aspx and the paging load on demand sample in the WebGrid sample VirtualLoadwithCustomLoadonDemand.aspx, the sample demonstrate load on demand virtual page, however it should be similar with classic paging.