If insertion order is important to your application -- and nothing in your post suggests it ought to be -- maybe you should consider using a 'Capped collection':

Capped collections MongoDB supports fixed-size collections called capped collections. This type of collection maintains insertion order and, once the specified size has been reached, behaves like a circular queue.
With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

The start of some sanity?

In reply to Re: MongoDB insert order by BrowserUk
in thread MongoDB insert order by PhilipJ

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