I’m REALLY happy with the Blackmagic Intensity Pro 4k PCI-E card. $199
On Win10 & can use their utility or Premiere to capture. Of note, it allows recording & sending video out at the same time (full duplex or something) so it’s possible to be sending clips to LZX for processing & recording the LZX output at the same time from the same puter. Admittedly I haven’t messed with that much, noticed it lagged some and haven’t gotten around to toying with settings to see if that can be diminished. I rarely hit record (bad habit) so it fell low in the priority queue.
Can upscale real-time while recording too, again I never do that but works A-OK far as I could tell.