SQL Server 2012 :: Asynchronous Cursor Population Slow For Large Result Sets

so async cursor population is supposed to create the cursor and return the cursor id quickly, while the server works on async populating the results. For a keyset-driven cursor, SQL Server stores the key sets in tempdb, which it then uses to fetch data for cursor results. Anyway, this works fine for smaller tables, but I'm finding for large result sets, the async cursor population is very slow and indeed seems to approximate synchronous time. The wait stat I get while it is running (supposedly asynchronously) is TRANSACTION_MUTEX.

Example:
--enable async cursor
exec dbo.sp_configure 'cursor threshold', 0; reconfigure;
declare @cursor int, @stmt nvarchar(max), @scrollopt int, @ccopt int, @rowcount int;
--example of giant result set
set @stmt = 'select * from sys.all_objects o1, sys.all_objects o1';

[code]...

Note that using the SQL "select * from sys.all_objects o1" is much faster than "select * from sys.all_objects o1, sys.all_objects o2". However, if cursor population is async, I'd expect the time to return a cursor id to be similar between the two.