super 8 kodachrome maxes out at around 1440×960 pixels ..
i have found that old 16mm B&W from 1940 does not have same resolution as 1980’s B&W .. IMO the 1940’s does NOT have the resolution to take full advantage in a 1920×1080 clip (adding to it could be the old lens ?)…
i have had the 1980 B&W scanned 2k res and it does hold ..also i have telecined 4×3 16mm using inverse anamorphic then taking a 16×9 out of it and it holds up excellent ( little better then if you had it telecined 16×9) .
just guessing i would say that the 250D can hold its own in a 1920×1080 frame = you will see a huge improvement over 720×486 …
if you want a better image you could transfer 10bit 1920×1080 24p, 4:2:2 color space to hard drive … you could then render out to either HDcam, D5 or DVCproHD or 24p for a film out… the HDCAM is 8bit 1440×1080, 3:1:1 color space 29.97 to tape .