My line started at 40/2 without interleaving, and ran like that for 2 days. However, it ran with about 4% packet loss - as seen on the BQM, and measured (at the end of the period) by my SamKnows box.
In this time, the profile was 38717, but I could only get speedtest results (from speedtest.net) of around 34.5Mbps. I guess the packet loss was stopping the tester working flat-out.
After exactly 48 hours, DLM added interleaving, so the latency change was immediately noticeable on the BQM - and this killed off the packet loss immediately.
I did speedtests that confirmed the Profile was still 38717, but it didn't seem to give any faster throughput.
Later on in the day, DLM intervened again, and gave me a lower sync - where the Profile was now around 34800. Speedtests then dropped to around 33.5Mbps.
This went on for a day, but I was then regraded onto a 10Mbps upstream. That obviously reset DLM entirely - because I went through the exact same set of events a second time.
BQM on day 1
BQM on day 3
BQM on day 4
, regrade just after midnight
BQM on day 6
Interesting that you've seen a gradual increase in latency, while I've seen a sudden step change.