lower downstream sync speed

[#1]

Is it possible to lower my downstream sync speed, either by a telnet setting on my unlocked HG612, or by intervention from Plusnet service?
I am on the 40/20 package, and synced at 72629.  I assume that a lower sync speed of say 55000 would not impact my 40Mb real world speeds, and give me a higher SNR and lower error rate thus considerably reducing the risk of DLM putting me on interleaving.

[#2]

I don't see the benefits to lowering your downstream sync speed (you would need to be put on the 40/10 variant).
The SNR is always the same - target is 6.

[#3]

But if the target margin could be raised the sync speed would be lower so fewer errors would be expected.
I've done exactly this on my Fritz!Box7390 (they make it easy by providing settings in the GIU) as I'm also on the 40/20, previously syncing around 60-65Mbps but now I have a target SNRM around 10dB with a resultant sync of about 53Mbps; this has, indeed, reduced my error rate (though so far it's only removed interleaving on the upstream).

[#4]

Does the 7390 give you a breakdown of the error count?