WPF ListView Very Slow Performance - Why? (ElementHost, or Other Reason?)

Use virtualization

<ListView ItemsSource="{BindingNames}"Name="lv">
            <ListView.ItemsPanel>
                <ItemsPanelTemplate>
                   <!--<StackPanel/>
                    If StackPanel was used, the memory consumed was over 2GB and dead slow.
                    -->
                   <VirtualizingStackPanel>
                    <!--Memory footprint is only 200 mb-->
                    </VirtualizingStackPanel>
                </ItemsPanelTemplate>
            </ListView.ItemsPanel>
            <ListView.ItemTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding}"/>
                </DataTemplate>
            </ListView.ItemTemplate>
        </ListView> 

You may also want to check this excellent article on the Code Project:

WPF: Data Virtualization By Paul McClean http://www.codeproject.com/KB/WPF/WpfDataVirtualization.aspx

It show you a much better approach at minimal memory and bandwidth usage.