ah, forgot about the HDPVR. I don't have one, but I remember that being a feature of it saving in h264 if desired, correct? The compression makes a huge difference as expected, and the quality is usually quite high with h264.
I have found that h264 video files which are played at a client can be fairly intensive to decode and display, especially for some lower end systems. My Dell SFF system has a good CPU, but onboard video and you can hear the fans crank up with just about any video stream. Sometimes the streams can get stuttery having to decode some highly compressed video.
Hence my recommendation to the OP to just buy a 3tb drive and be done with it, meaning don't even compress. (Or two, as I like to have redundant RAID drives and keep the system up without losing anything.) I have found with my 4TB and years of recordings, even after compression there's not enough room.