I have owned both SD and HD CRT RPTV’s, SD running native on the SD set suffered from visible scan lines at my viewing distance. Upscaling SD to 1080i for display on the 1080i HD set was a HUGE improvement, scan lines where no longer visible and the image was much smoother and more film like, no way I would ever want to display SD natively at the screen size- viewing distance ratio I use.
I still have a 36” HD direct view CRT which is a true multisync display, its just like a PC monitor and will run any combination of refresh rate and resolution within its bandwidth limitations and supports 480i/p 60Hz 576i/p 50Hz, 720p 50/60Hz and 1080i 50/60Hz as well as many other unusual combinations natively. The best picture quality is obtained by running at the displays sweet spot which happens to be 1366x768. Scaling SD source up to that resolution via my HTPC looks significantly better then displaying it at its native resolution, cleaner smoother picture with no visible scan lines.
My main display is a modified 70” Sony SXRD XBR2 and SD upscaled to 1080p looks better on it then any of the CRT’s running native or upscaled.
Since the SXRD has optical overscan like all RPTV’s I downscale 1080i and 1080p video slightly to fit the visible screen area, again using a PC, and there is no perceptible degradation to image quality in doing so even though 1:1 mapping is lost. If anything, the slightly downscaled image looks a little sharper as it is smaller. PC generated text and graphics have nothing in common with video, if you have good scaling you don’t need 1:1 mapping for video.
I have been heavily involved in video scaling on PC’s for many years and started the whole FFDShow scaling-sharpening thing that swept through the Home Theatre PC community several years back and I have never found an instance where upscaling did not result in a better picture.
Running SD natively on a 65” -73” display like the Mitsubishi (even if it where possible) is something I would rather not contemplate, the word ugly comes to mind unless you where seated so far away that the TV looked small.