Had the TP-Link MR600 for a few months now and there's been a few issues bugging me.

I used to get between 80-100mbps quite consistently but since last month i've not been able to get above 50.  My upload speeds have tanked from average 50 to about 9. Average ping has gone from about 20 to 40, Now, these are still great speeds and Im not looking a gift horse in the mouth, BUT, I do pay £50 a month and i was getting some nice speeds before.

I cant help wonder if theres a technical issue causing this or a setting in the router I can tweak to get my old speeds back.

There was an incident a few weeks ago where i got chucked onto 3G speeds for about a day and oddly enough, my 4G+ icon was on, which it usually isnt.  Despite the 4G+ light being on, i was getting very poor speeds which i reported to EE.  They fixed this and boosted back up to 4G however at much lower speeds than my first few months. Should I be getting 4G+?  Or is that determined by the nearby mast?

I've also read on here about the Band.  I'm currently on Band 3 but is there a way to change this or again, is this determined by the mast?  Doesnt look like i can change it in setting anyways.

To summarise:

1. Should I be concerned about not getting the 4G+ to work?
2. Are there any settings in the MR600 that i can tweak to get better speeds/ping?
3. Is it worth turning off NAT Boost and trying QoS to improve gaming ping etc?
4. Is it worth contacting my provider to try and get better speeds as there is certainly something going on with their service or the mast.