57 is mistaken on this issue.
MTS uses Harmonic DiviCom Electra 7000 Encoders. These units encode incoming video into MPEG-4 format on a per-channel, not per-user basis. The target bit-rate of each channel can be adjusted by the telco so that the resulting stream will not exceed the allocated bandwidth. That is why different telcos can have a different number of hours per GB of disk space.
Secondly, MTS uses VDSL2 and allocates about 35 Mbps of bandwidth consisting of 24 Mbps for IPTV and 9.5 Mbps for standard internet (7.5 down and 2 up). For the typical internet user there will not be a conflict between IPTV and internet use.
For those internet users that order the 32 Mbps internet service, IPTV takes priority over internet use. "This package leverages any unused bandwidth not used by the MTS Ultimate TV Service to be used for Internet."
Mike, to confirm that you have the VIP1216, press MENU, Settings, General, System Information and look on the System Info screen for the line that says "Set-Top Box/CPU". Motorola also makes a VIP1225 with a 250 GB drive, but MTS does not distribute that unit to the best of my knowledge.
To further explain why there can be some variation in the number of hours that fit on the PVR, if the encoder is optimized for fast-moving action scenes, then it is possible that programs that don't have a lot of action will take less space. Also SD commercials inserted into a HD program will take less space.
One other tip: Unless all your programs are marked as "Keep until I erase", the oldest programs will be erased when the available space reaches 10%.