[neonz80]

I've been using the OSSC to upscale a 50 Hz RGB signal (SCART) to 1024x1024 (256 lines duplicated 4x). Both my HDMI capture cards happily accept that resolution with the right software.

I haven't tried the OSSC Pro, but the Retrotink 4k should probably also work fine and is really easy to use. A bit on the expensive side though...

[snvzz]

I already wouldn't touch the retrotink simply because it isn't open hardware, but it also is not anywhere as configurable; It's meant for non-techie people who want to be abstracted from the details.

Definitely easier to use, but nowhere as flexible.

[neonz80]

I do not find the Retrotink 4k any less configurable than the OSSC (non-pro, I haven't tried the pro). Note that the 4k is nothing like the 5X-Pro which is more plug and play.