I just got cable internet installed (Comcast). It claims that my down speed should be 25mbit. Over wifi, I get close to that on my laptop, but only about 8 on average with my iPhone/iPad.

I'm using testmy.net in the browser on all devices. I have an ARRIS / Motorola SurfBoard SB6141 DOCSIS 3.0 Cable Modem and a Medialink Wireless N Broadband Router.

I read somewhere that disabling WMM and the firewall on the router would help (is this even a safe idea?). I've tried both, and neither seem to make much of a difference, if any at all (sidebar: I've noticed that my download speeds vary wildly with cable internet... on my laptop, I'll get 12 down, then 22 five minutes later. Is this typical for cable internet?).