The dual-SIM feature could end up on the OLED models already leaked a week ago. the gigabit LTE speeds will be provided by the Intel XMM 7560 and Snapdragon X20 LTE chips.
https://www.notebookcheck.net/New-iPhone-models-with-dual-SIM-option-and-Gigabit-LTE-are-expected-to-launch-in-2018.264398.0.html