It depends on how the post processing effects work. Bloom and DOF might be diminished if you render at higher res and then down-sample it.

cool. where is the slider in the project settings. cant find it.

This is a 7 year old thread, also, there is none, change it via scalability file (to test use console commands, for custom scalability, copy basescalability in engine to project config, rename it DefaultScalability.ini), change whatever commands of taa you want, use execute console command to switch methods. TAA is fixed cost, change it to whatever looks best cross-system, many samples can blur, low samples wont take care of edges. The default is a good balance, but if it blurs, and changing stuff doesnt do much, or it gets jagged edges, feel free to tweak things by hand.