Well, I've been doing some 4G testing on my new EE SIM and so far, all is good!
There's one mast on the A1, North of Stamford, and that game me 92Mbps down and 46Mbps upload! Awesome!
Also tested what was an old Orange mast near Colsterworth, and got 41Mbps down and 37Mbps up.
The mast in Metheringham, Lincolnshire was also tested, though I wasn't actually in Metheringham for the vast majority of the day. The signal strength was about 2 bars, and the mast provided 59Mbps down, and 6.5Mbps up. Interestingly, 3G in this location (again 2 to 3 bars, so 3G was slightly stronger) provided 8Mbps down and 2Mbps up, which again wasn't bad. I suspect that it would easily have provided 10-15Mbps down on 3G in a stronger signal area. As for 4G on that mast, I did test it whilst passing the mast (so strong signal area) and got 58Mbps down and 35Mbps up.
So far so good. Although, on this new SIM, I have to choose between pure 4G testing (in which case, stick it on LTE only), streaming reliability (3G only), or general testing (default mode). I can't keep my S4 in default all of the time, due to how it likes to jump to EDGE/GPRS, despite 3G (or even 4G) being present, albeit at a weaker signal strength.