I dont think it should drop that fast either based on what little you were doing, you mentioned that you have a Iphone, what model? the reason I ask is because the IOS 8.0.0 - 8.0.1 had issues with wifi connections and can cause data lose due to retrying to connect, keep in mind im just guessing here. what I would suggest next is to only connect 1 computer to your router and do some browsing and see if your data seems to be dropping at what you would call a normal level, if 1 computer does ok then add the other one and see, if its ok with the 2nd computer then add your other computers or devices 1 at a time until you start seeing the data dropping at that point remove the devices 1 at a time in reverse order to see if the drop stops. another option is to download a program Net Guard here is a link to it and its free. you will need to install it on all computers you connect to your router and it will tell you what programs are using data and how much. unfortunately Im not familiar with this software but there are a couple of other customers on here that know it very well, they are Gwalk900 and sgoshe they can help you understand how to read it.
http://www.cucusoft.com/netguard.aspx
