I have a 50 inch Panasonic st50 and plan on buying a Yamaha 673 receiver. Will I notice a difference because it upscales to 4k resolution.
That option is only for 4K tv's, not 1080p. What you will notice a difference in picture is when you enable the 1080p up scaler on the receiver, if it has a good chip that is and apply proper settings.
TV - Panasonic 55GT50 THX, Main Speakers - Klipsch Gallery G28's, Center Channel- Klipsch RC-52, Sub-Klipsch Sub 12, Surround - Klipsch RS-52 II Bluray/Game - HTPC/PS3, Receiver - Onkyo RC-360, HTPC- Intel Core i3, HDMI,Windows 7,XBMC,Bluray,7 TB, Video Processor -Darbee
I actually have (downscaling 1080p to 480i) and the improved chroma and cleaner image (fewer artifacts) was an improvement over DVD.
Oh yeah, it'll be an improvement alright. But that's from the disc, it won't turn your TV into something better than it is.
In other words, your TV won't upscale to 4K, so there's a good chance that unless you're playing 4K material (less compressed, better master & higher bitrate), it'll look better. If you try and upconvert a 1080p Blu-ray disc, I don't know if there will be a single difference. You'll need a 4KTV for that.