I wanted to see how difficulty affects some of the times for a few of the levels where the route is quite fixed.

Mission 1 on Insane does require a divergence from the Normal and Hard routes as its less viable to split the squads up. Even with cover bonuses the Force Commander and a single Tactical Marine squad aren't quite enough to clear out the middle base quickly or cleanly. I tried morale shocking and then ignoring the Shoota squads as that block new spawns but it never quite came together. I should also say this run was far from perfect, but it it principally for comparison to other difficulty so an approximate time is fine.

Overall about 1 minute slower then Normal mode and just under thirty second slower then Hard mode.