There is obviously a reason why you are looking at 800Mhz (Band 20) but this is probably the worst EE Band for Data use on a Router, if it is only Band 20 available to you then it's normally in use by EE as an In Fill Site or Extended Coverage usage or other specific reasons.
Band 20 on EE generally only operate on 5Mhz Bandwidth and sometimes without Carrier Aggregation and or MiMo so you could be looking at some really low DL Speeds over normal.
Are you sure that B20 is only available to you, do you want to Post up an approx location (Not Full Address) or a Post Code near you, if so maybe we can look into this a bit more, or you could PM your Postcode.
Most of the Early EE MiFi Devices did not cover Band 20, but pretty much most Routers for the UK or EU now do.
Another option subject to your location, may be to source a Device that gives External Antenna Port options.
Normally I would say go for a LTE Router that is at least CAT16 Spec in order to take the full opportunity of what the latest 4G Trickery has to offer, but it would be nice to move forward armed with a bit more knowledge of what Coverage and Bands are available to you in your Area.
