I don't think it has anything to do with network saturation. I'm currently the ONLY one in my neighborhood that is utilizing the 5ghz band, and I have these issues all the time - regardless how far away or where my router is located. Exact same issue at work, where I can't even count the 5ghz networks in reach. Performance is just fine in either place, until you hit these spikes. Sometimes they result in connection drops, most of the time "just" crazy long lags. I notice these lags even during regular web browsing if I happen to try access a page when they happen.
This card is nothing but garbage... I wish intel would refund me the $35 or whatever I paid for it. Obviously they are not able to fix this issue.