The AA usually bottlenecks CPU (and in some cases the GPU), provocating a slowdown. And yes, it seems that your system can´t handle 8x AA while keeping high speed.
Rig 1: Windows 10 Home | AMD A6-1450 @ 600/1000/1400 MHz | AMD Radeon HD Graphics 8250 | 4GB RAM | HP Pavilion TouchSmart 11.
Rig 2: Windows 10 Pro | Intel Core i7-2640M @ 780/2800/3500 MHz | Intel HD 3000 Mobile | 8GB RAM | Dell Latitude 6320.