So I did what I should have done before, and just created a plugin to test this.  This is running on CRM 2013 on my local VM (Pre-Operation), so results can vary, but I'm seeing plain old Create taking about 290ms less per 100 entities
I first created this plug
public class ExecuteMultipleTester : PluginBase
{
    protected override void ExecuteInternal(Common.Plugin.LocalPluginContext pluginContext)
    {
        var watch = new Stopwatch();
        var service = pluginContext.OrganizationService;
        watch.Start();
        var request = new ExecuteMultipleRequest
        {
            Settings = new ExecuteMultipleSettings
            {
                ContinueOnError = false,
                ReturnResponses = false,
            },
            Requests = new OrganizationRequestCollection()
        };
        for (var i = 0; i < 100; i++)
        {
            request.Requests.Add(new CreateRequest
            {
                Target = new new_Year
                {
                    new_Year = i + "- B",
                    new_YearIntValue = i,
                }
            });
        }
        service.Execute(request);
        watch.Stop();
        var multipleCreate = watch.ElapsedMilliseconds;
        watch.Restart();
        for(var i = 0; i < 100; i++)
        {
            service.Create(new new_Year
            {
                new_Year = i + "- A",
                new_YearIntValue = i,
            });
        }
        watch.Stop();
        throw new InvalidPluginExecutionException(String.Format("ExecuteMultipleRequest Time was: {0}ms, Standard was: {1}ms", multipleCreate, watch.ElapsedMilliseconds));
    }
}
Registered the plugin and ran 10 tests.  Here are the results (ASCII tables, oh yah!):
+------------------+---------------+-------+
| Execute Multiple | Sevice.Create | Diff  |
+------------------+---------------+-------+
| 777              | 408           | 369   |
| 493              | 327           | 166   |
| 614              | 346           | 268   |
| 548              | 331           | 217   |
| 577              | 312           | 265   |
| 675              | 313           | 362   |
| 574              | 318           | 256   |
| 553              | 326           | 227   |
| 810              | 318           | 492   |
| 595              | 311           | 284   |
+------------------+---------------+-------+
|                    Average Diff: | 290.6 |
+------------------+---------------+-------+
So from these results, there is no need to execute an ExecuteMultipleRequest from within a plugin.  You're already on the server, having to execute more code to perform the same operation.
Update 1 - 1000 Creates Test against a full environment
I ran this test again for the creation of a 1000 records, and in a full fledged environment with separate boxes for SQL, Services, and Web.  Very similar results (only ran 5 tests since it was taking a lot longer)
+------------------+----------+--------+
| Execute Multiple | Standard |  Diff  |
+------------------+----------+--------+
|            18922 | 15057    | 3865   |
|            18668 | 14946    | 3722   |
|            18162 | 14773    | 3389   |
|            19059 | 14925    | 4134   |
|            18334 | 15306    | 3028   |
+------------------+----------+--------+
|                  | Average  | 3627.6 |
+------------------+----------+--------+
Interesting thing was the time was around 25 times longer for 10 times more records, but the differences was only 12 times more. ( Attempted to do updates rather than deletes, but I kept on getting timeout errors, even at just one for each...  Must have been creating some sort of infinite loop, just not sure what... )
For a 1000 creates, its almost 4 seconds slower.  I wouldn't use it in my plugins...