Paying for business 50/10, but never get any better than 31/7: Is this normal?

I'd like to understand from others, or CC people whether this is normal. I would expect, in particular middle of the night, to get close to advertised speeds.

If this is not normal, will a service call get it sorted out? While I would be at it, can I get my modem replaced so I can get proper DHCP6-PD delegation (the SMC does not do it right, and after 2 onths working with them CC still has not sorted it).

Since somebody is bound to ask:

SMC D3G gateway in bridge mode -> Ubiquiti EdgeMax PoE (which will route at 1Gb speeds) Gb link -> Gb link wired to Gb switch -> wired to computer used for test. All links verified to be full duplex at 1000.

Signals:

Downstream Channel

It would seem that the above should support 4 * 5.3Msym = 4 * 5.3 * 8 Mbps: about 170Mb/s. I understand I will be throttled because I do not fork over enough dollars at $130+/mo, but if the bandwidth is there, I'd expect to get what I pay for.

Upstream Channel

Upload avail: 3 * 2.5Msym * 6: About 45Mbps, also plenty to provide 10Mbps as promised