Will Comcast migration to MPEG-4 HD changes recording file size.

Have a Roamio Plus, upgraded to 3 TB. Currently 1 hr of HD recording runs anywhere from 5-8 GB. Comcast here in Atlanta area is moving HD programming to MPEG-4 format. Will that effect the actual recording file size. EG number of recordings per TB. Just wondering if the old number of shows per TB rule of thumb will change. Probably lots of cheap Series 3 HD's will be hitting the market soon.