@benzi
Hey
To be honest, its likely the AP is causing this.
The EAP110 is a older device now and run on the 2.4ghz frequency, this is known to be much slower than the advertised speeds due to congestion. Sadly its a common issue with this grade of hardware and cant really be massively improved.
If you have 100mb internet now, you should be considering upgrading this device to at least a EAP2xx model (225 Outdoor for example) as this supports 5ghz which will give you the speeds you are after.
In terms of the CAT6 cable, cat6 is backwards compatible so its not an issue.