I think the results you get depend strongly on the chipsets the TV manufacturer has used in their TVs. I own two HDTV's: a (nearly) 6 year old Samsung 720p DLP (HLN series) and a brand new Sony Z series 1080p, and there is a world of difference in the picture quality I get in RTV playback.
In both cases I have my cable box going into the RTV via composite video, and the RTV out into the TV as 480p component video.
The first observation is that, when my cable company switched from analog to all-digital cable (and I got a converter box), the picture quality (with the RTV set at "Medium" quality) improved somewhat on the Sammy.
But what amazes me is the PQ I get on the Sony with the same setup: again with a "Medium" quality recording, if the show is letterboxed, I can put my Sony into "zoom" mode and fill the screen with an incredibly nice quality image.
To me this says the Sony does a much better job of up-scaling 480p to 1080 than the Samsung does going from 480p to 720. Now, six years of progress in scaler chips has got to be worth something.
Then too, I think a lot of this is due to the fact that it's digital cable coming into the RTV as composite video, not analog dependent on the RTV's crummy NTSC tuner.
But either way, it's a pleasant surprise with the new Sony.
So, Johnny, what's the input to your RTV? If you can switch to something better than RF input to the RTV's tuner, you might be pleasantly surprised.