I have 600mbps wired via cat8 Ethernet cable my speed is fine but for gaming I have high latency and packet loss have tired all the fixes. I spoke to virgin customer service on phone they advised posting on here and maybe booking a skilled technician in this field hoping for the fix as the speed and service is otherwise great.
If I were you, I would start by taking a look at the various threads in the 'Online Gaming' section of this forum - quite a few of them, you will find disturbingly familiar.