When I turn time acceleration on, I get a heavy frame drop, from 100+ frames at 1x to 6 frames at 2x. This occurs in every map, with a blank mission or a heavily populated mission. The actual time acceleration speed seems to cap at 2x. Going to a higher time acceleration (2x+) only increases lag, but doesn't actually "speed up". It occurs in first person, F2, or F10. It also occurs without a player aircraft on the map. A few months ago on the same PC I was able to get up to at least 10× and maintain a smooth experience.