Who's saying 4K would beat plasma?
OK about the HDD. That's all about what the smart tv can do. It's not a PC and I find most of the smart tvs to be pretty bad in this area. There are limits all over from file systems (FAT, NTSF, other) to size limits, encoding issues, and one major line would not see a lot of USB 3.0 drives. I find an old 500GB USB 2.0 drive to work most of the time.