Speeding question, " vs '

Hi!

It just crossed my mind, that I usually do it like this:

$whatver=$_POST["returned_value"];

instead of

$whatver=$_POST['returned_value'];

The latter should be faster, as within ' nothing is replaced as in ".
I now wornder, what difference this makes in speed?
It should make some, but not really.... then again, with 10000000
users, it might.

What do you do?

WBR
Sonnich
.