hi there,
my download speed was 16 MBPS / sec after upgrading to ios 6.1.2 ( İn Turkey , 3G double carrier good for speed and my iphone was using that)
i realized slow connection and tested, i m getting under 1 mbps now .. 
as in the picture, u can see the difference between; 15.01.2013 and 24.02.2013 plz help