If I were you I'd disconnect the extention for a few days and see what happens rather than try another pair.
Thanks to everyone who helped with this.
Woke up this morning, got dressed, brushed my teeth, checked my router stats (it's incredible I am still married) and I am back up at a sync of 80 and actual speed of ~77. Not sure how/why this happened or happened so quickly but it has.
Now just to get the extension wiring sorted. Thanks again.