Projector user here, using a 4096x2160 native D-ILA on a 120" screen. I can only get my old DVD rips (852x480 2.5 mb/s 264) to look somewhat decent by sitting in the back row and just letting my poor vision fill in the gaps. The best upscaler I've seen is madVR running on an HTPC - it's actually better than the upscaler in my Oppo UHD BD player, which itself is pretty good. MadVR also does a phenomenal job of expanding BT.709 content to the native BT.2020 color space of the 12-bit LCoS imagers. However, not even madVR can work the absolute magic required to make 480p DVD rips look decent on such a big screen.*
Really, this setup needs at least 1080p to shine, and in the front row you can usually see the difference between 1080p and 4K video content. However, some older flicks just have that warm, soft look to them; other than the increased color space and bit rate provided by 4K discs/streaming, they don't really benefit from the increased resolution.
For modern computing, 3840x2160 @ 125% on a 32" screen is where it's at. For retro Win98-XP gaming, 1600x1200 on a 21" 4:3 CRT/LCD (or smack dab in the center of a 24" 16:10 LCD scaled to pixel perfection) is where it's at.
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* I have been experimenting with AI upscaling, encoding the upscaled output as 10-bit HEVC at 1080p24 (or 1080p60 for NTSC-sourced DVDs). They do look appreciably better than my old 480p 264 rips--especially the 60p ones, which now retain the super smooth motion of the original DVDs. When I originally ripped these discs back in 2007, I made the mistake of encoding NTSC-sourced DVDs at 30fps. That said, I'm not sure it'd be worth the time to upscale all of my old DVDs. Actually, I know it wouldn't be worth the time - it's just kind of a fun experiment. Whenever I get the urge to watch an episode of Home Improvement, I'll just put the disc in my PS2 and watch it on the old CRT television. 480 over component still looks pretty decent to these standard def eyes.
94 MHz NEC VR4300 | SGI Reality CoPro | 8MB RDRAM | Each game gets its own SSD - nooice!