By using internet speedtest under a variety of the settings the following was found (this may not hold true in the future but its what seemed to make sense at the time) :
1 Wireless WMM (QoS)
Enabling QoS means that VOIP/videos/games take priority and can cause issues for web browsers when gaming is in progress. Heavy gaming seems to even stop connection to the wireless network (at that time the specific game causing problems was DOTA 2).
Switching off QoS leaves all network connections the same access to the internet causing lag problems for game users/video watchers.
Channel (1,6,9,11 are supposedly best for less interference) Is significant with 6 significantly better on the 2.4GHz band for our particular wifi network at the current time. Wireless phones and microwave may interfere along with other local wifi networks.
Unsure of 5GHz band cos not sure what uses it, channels 36,40,44,48 recommended so stuck it at 40 (from 112)
3 Other settings had little or adverse effects
tried 40MHz, 20Mhz, 5GHz off
switching off various devices
moving all electrical items from around the router.
4 These are the current working settings :