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[#1]

Can you see if things remain stable for a week or so then if they do you could request a noise margin reduction.
Given the downstream attenuation that sync speed is superb for a 14dB noise margin although your upstream attenuation seems high.

[#2]

Hi John,
you need to get rid of the connections on 3 & 4 at the extensions as well as the master. Jim has already commented on the Upstream Attenuation which needs a bit more investigation. Those Solwise filters you are using aren't the best in the world, but deal with the wiring first and do a daytime resync and see what the latest stats are like.

[#3]

half an hour grovelling around on a saturday morning, all my extensions are now reduced to simple 2 & 5 connections.
there's already some improvement according to the router: 
Modem Status

Connection Status Connected
Us Rate (Kbps) 448
Ds Rate (Kbps) 4096
US Margin 22
DS Margin 15
Modulation MMODE
LOS Errors 0
DS Line Attenuation 48
US Line Attenuation 53
Path Mode Interleaved
DSL Statistics

Near End F4 Loop Back Count 0
Near End F5 Loop Back Count 0
john

[#4]

Hi John,
well that's starting to look better, now we need to try and find out why the reported US attenuation is so high, the cause of  which could also be affecting your sync speed. It could be any of the following - 1) Poor/faulty filter(s)  2) Faulty Modem/Router  3) Faulty Line  4) Fault at the exchange.
The easiest to check out first is filters. I'd suggest you borrow an extra pair of hands for a few minutes to avoid too many re-syncs in a short time interval - I'd usually say no more than 5 in an hour then leave it alone for the rest of the day so that the exchange DLM equipment doesn't think you have an ongoing problem.
You need to unplug everything apart from the Filter (and phone on it?) that the router is plugged into
As unplugging something may cause a resync, if the extra pair of hands unplugs one lot at the same instant as you unplug the other, if there is a resync - it's only one hopefully. Once all the rest is unplugged (if a resync did not occur then re-boot) then immediately grab a set of Stats to post.
Do not get the filters mixed up. Take one of the other filters and substitute it for the one the router is plugged into, but do not plug a phone into it. Grab another set of stats to post. Now plug a corded phone into this filter, if there's a resync grab the stats, otherwise pickup the phone and check there isn't a resync or line noise. (Stats if there is.)
Finally take the remaining filter and substitute that but again with out plugging the phone in to start. Grab a set of stats, then plug in the corded phone see if there is a change etc as before.
Post all the stats & info.