Hi I'm a newbie here. I bought my first iMac (late 2013) after using iPhones/iPads and am finding that the wireless download speeds degrade significantly over days. I normally get 65-70 Mb/s but with my iMac this slowly degrades to 20-30Mb/s over a few days. The problem is rectified by switching off and restarting WiFi. However I am sure I should not have to do this. Any suggestions ?