FWIW, I get bobbins speed from the hub to my iPhone and iPad too. Makes no difference if I use 2.4Ghz or 5Ghz (that the iPad should love), 54, 145 or 300 mbps. It's just rubbish, even when I'm sat on top of it. Laptops and Xboxes in the house are fine (in the most part) though.
As your iDevices are your only means of connecting wirelessly, can you be sure you've no interference from anywhere? I had our hub out of the way in the kitchen once over and if you were on the wrong side of it, it would crap out. Reason: big stainless steel fridge freezer next to it
Although not the point, I don't usually download on the iPhone/iPad anyway so it doesn't worry me. Youtube can be a drag though..