68meg at 600m is mighty impressive.
To paraphrase an estate agent: Gauge, Gauge, Gauge.
Attenuation is 19dB, which is exceedingly low for 600m. I suspect some fat cable might be being used... possibly even 0.9mm copper.
In comparison, my second line had an attenuation of around 16dB, and was approx 375m from the cabinet. That was quite good performance for the distance, and I occasionally wondered whether that was fatter than the standard 0.5mm
My third, current line has an attenuation of 8.5dB, but is only 100m. I strongly suspect that this is thinner (0.4mm) copper though. If so, it would act like 150m of standard 0.5mm copper.