Demonstration of using async to grab a bunch of Sitecore queries in parallel Performance on a dual-core machine appeared to be 30-100% faster than iterative.

async.cs

using System.Linq;
using Isite.Sitecore.UI.WebControls;
using Isite.Extensions;
using System.Web.UI;
using System.Threading.Tasks;
using Sitecore.Data.Items;
using System.Collections.Generic;
using System.Threading;
using Sitecore.Caching;
using System.Diagnostics;

namespace AsyncTest
{
	public class AsyncTest : WebControl
	{
	        private List<Item[]> _taskResults = new List<Item[]>();
	
	        protected override void OnLoad(System.EventArgs e)
	        {
	            // the RegisterAsyncTask() method allows us to register something to run asynchronously
	            // from an event handler that would otherwise have to be async void (which is EVIL)
	            // This task will begin executing now, and be completed prior to Render()
	            Page.RegisterAsyncTask(new PageAsyncTask(Asyncer));
	
	            base.OnLoad(e);
	        }
	
	        private async Task Asyncer()
	        {
	            List<Task<Item[]>> foos = new List<Task<Item[]>>();
	            CacheManager.ClearAllCaches(); // start with empty Sitecore caches
	
	            // For test data we'll grab every item in the database, split up asynchronously by children of /sitecore
	            var rootItems = Sitecore.Context.Database.GetItem("/sitecore").Children;
	
	            var sw = new Stopwatch();
	            sw.Start();
	
	            // ASYNC - go get the children of the root in parallel
	            // note: it's actually kinda important to have the lambda in there that calls Acquire()
	            foreach(Item root in rootItems) {
	                foos.Add(Task.Run(() => Acquire(root)));
	            }
	
	            // wait till all the async queries return
	            var asyncResults = await Task.WhenAll(foos);
	
	            _taskResults.AddRange(asyncResults);
	
	            sw.Stop();
	            Page.Response.Write("Async in " + sw.ElapsedMilliseconds + "ms <br>");
	
	            CacheManager.ClearAllCaches();
	            sw.Restart();
	
	            // SYNCHRONOUS - get all children iteratively
	            foreach (Item root in rootItems)
	            {
	                _taskResults.Add(Acquire(root));
	            }
	
	            sw.Stop();
	            Page.Response.Write("Sync in " + sw.ElapsedMilliseconds + "ms <br>");
	        }
	
	        private Item[] Acquire(Item context)
	        {
	            return context.Axes.GetDescendants();
	        }
	}
}