Based on a topic you previously created (
https://forum.kitz.co.uk/index.php/topic,22130.0.html), the sync rate already dropped below 79999 Kbps prior to the socket change (78515 Kbps in your post), unless I am missing something. So while it is sat at 78083 Kbps now, there is nothing to say that the NTE5A/MK2 would have given anything more than perhaps a subtle couple hundred Kbps (and you're less than 2 Mbps below the maximum anyway). The only thing I would be concerned about is the error rate perhaps being higher since the construction of the NTE5C is questionable (I have one and I think the other line with NTE5A/MK3 might be faring better, though that's not scientific).
I think the order of events went like this:
1. Your modem resync'd and you fell ~1.5 Mbps below the maximum possible sync
2. You got worried about it and changed your socket on a whim
3. You gained nothing and perhaps even lost a tiny bit
4. Regret?
But
please understand that I am not trying to patronise you at all. I think you're getting a bit too worried/obsessed about how many bits are coming down your line. Maybe close the router statistics page and take it out of your favourites to stop impulsive viewing? The last post in the other topic made me think that you were no longer worried about it.
Still got old master socket MK2 as ex engineer gave to me. I kept in the wall cupboard. But, the problem is can't put it back in because the wiring feed in the back of MK4 are remain BT property as I am not allow to touch it.
I also imagine the ex-Openreach engineer shouldn't be allowed to touch it either, but it didn't stop him?
Though, perhaps it would beneficial just to leave it alone unless you really feel the current setup is adversely impacting sync speeds and stability
beyond reasonable doubt.