Hey, try Alsace in 1918 if your PC struggles with frame rates in sections that have a large ground war ongoing.
Mud Wasp, Alsace works just fine for me. It actually runs faster in 1918 than Flanders in 1915 during an offensive. It's a quiet region, where nothing happens and with all the forests your biggest worry is where to put down your wounded bird without crashing.
Plenty of pretty birds to take from the air down there. Quiet....?