No improvement in the following PLINQ code

I do not see any improvement in processing speed using the following code:

IEnumerable<Quote> sortedQuotes = (from x in unsortedQuotes.AsParallel()
                                           orderby (x.DateTimeTicks)
                                           select x);

in serial version:

IEnumerable<Quote> sortedQuotes = (from x in unsortedQuotes
                                           orderby (x.DateTimeTicks)
                                           select x);

Am I missing something? I changed the number of elements in the source collections from thousands to several tens of millions, and the size did not show that the Parallel version is coming forward.

Any advice appreciated. By the way, if anyone knows a faster way to sort more efficiently (given my specified type of element variable (containing long DateTimeTicks, by which elements are sorted in the collection), that will also be evaluated.

Edit: “sort efficiently” → As fast as possible.

thank