I just did a quick range test with the CC1120 transceivers (our favourite for range):
at 2.2km it is easy to link even with omni antennas (-99dB) but a yagi was excellent (-89dB).
At 3.3km (not in good line of sight  and grazing wet ground) Yagi to omni was starting to loose packets (-106dB) and yagi to panel antenna was not much better but still communicating. This bodes well for a low power 868MHz network over the whole field site including our 3km link up from the valley.

This was at 50kbit/s using the CC1120DK TI test boards.

big round Omni was 4dBi gain

Yagi tested was 9 dBi gain

Panel was 7dBi gain