I got a nice fancy VGA capture card with generally good reviews from Inogeni. The images that come through on the thing are crystal clear, and look totally amazing, but it only works (on my DOS machine) in the 640x480@60hz mode that Windows 3.11 gives me. In fact, it seems to have issues with most of the DOS VGA modes, which are all in the 70hz range and higher.
By this point I've been through quite a few capture devices and format converters trying to find something or some combination of them that supports 70hz VGA modes. So far the only working option I've found is using a VGA-to-S-Video converter, then capturing the (fuzzy, low-framerate) S-Video output.
If I ever stream development on this game I'll be doing it through fuzzy S-Video goggles, I guess.