Just an update on this for anyone who may find it helpful in the future. I managed to pick up a Poynting 4G-XPOL-A0002 directional antenna second hand on eBay and have been doing a bit more testing. With this pointed at the nearest mast (indoors through a window) signal strength has improved significantly. RSRP is up around 10dBm, SINR is up around 10dB too (now typically 25dB). RSRQ was already pretty good but now hovers around -3dB. We’re still at the mercy of a busy network, but at least the connection is now really solid whatever the weather. During off-peak times, download speeds are up from around 30Mbps to 60Mbps which isn’t bad for the cheap little Huawei router. I’d definitely recommend a similar directional antenna to anyone in a similar situation to us and this Poynting unit has been excellent.
I’ve also had chance to do a bit of comparison between 3 (via Smarty) and EE. Both deliver 60+ Mbps download and 40 or so upload in off peak times and both vary quite a bit during the day. EE is definitely a bit more reliable overall though, at it’s worst moments, the speed never drops quite as low as we’ve found with the Smarty SIM. When I get chance, I’ll try some comparison of 3 vs Smarty to see if its the actual 3 network or just them throttling Smarty users.