Gigabit Broadband Cat6 Ethernet Speed Issues

[Richy_Mac]

I've had sky gigabit for a few months now and to begin with was running powerlines to my upstairs office where i work predominantly.  Speeds would hold around 60mb but there would be occasional dropouts to period of 1-5mb, these would often be for sustained periods (at least a day).  I've now had a Cat6 ethernet cable fitted today,  when i first booted up and ran a speed test i was getting 750mb (which I am completely happy with),  over the next hour this dropped substatinally and I'm now recordign 10-15mb.   The wifi conneciton on my iphone is picking up 400mb stood next to the router so unsure where the issue lies.  Any help would be apprecaited!

[jamesn123]

@Richy_Mac 

Do you have anything else connected to the ethernet ports such as a switch, Sky Q box etc?
Can you please post your router stats