Depending on how your wifi is setup and how your antennas are positioned, that alone could account for all the problems your running in to. Make an experiment of it. Do the tests and run some programs your noticing you have considerable lag on via Wifi. Then run a cable directly to your router from your computer, disable your wifi and do it all over again. See if it has any effect. If not then you've at least taken one factor out of the problem.