I had a bit of a play with 4G towards the start of last year - specifically with Three. There's a 7 page topic
here which documents my experience, along with replies from others who have contributed their own configurations and experiences.
My own experience condensed down would be that with the best positioning indoors using a dedicated modem, downstream speeds varied anywhere between 15-90 Mbps depending on the time of day. During the night, it would quite happily sit around 70 Mbps. However, during the day through to evening it could be as low as 15 Mbps, but typically somewhere between 20-40 Mbps if I recall correctly. Upload speeds were around 20 Mbps.