Problem with newly aquired N66U

Hi

I'm on the latest stable merlin firmware for this router. I have been having lag spikes every so often whilst gaming online. My ping just jumps. I'm currently using a cat5e wired connection. Upnp is off and Nat hardware accel is on. Also I dont use any qos but the firewall is on. I noticed that iphones and ipads might be contributing to the spike when they connect to the network.

Thanks
Andrew