Read through this discussion.
I have the same processor, paired with a 1060 (6GB)
A. not enough system ram
B. cpu is not fast enough to process it all in time
C. internet speed is too low (London needs 100mbps+)
Solution, fly slower. My laptop can only keep up at quarter sim rate in the Bonanza at terrain detail 200. It barely keeps up at terrain detail 50 at normal speed. Or turn PG data off.
London and the other new areas added in World update 3 are far more dense than the ones before, yet also over Rome I have to fly slower for the sim to keep up.