BM SDI CARD kills playback performance

I have two Mac 5.1 machines with near identical specs as below.
Same OS, same Titan X card and drivers.

The only difference is the other has 4x6TB HDDs in raid 5 and no SDI output card.
BM speed test of around 400mb/s

Same 4K XAVC files on both machines.

The HDD machine achieves almost instant 25fps in the edit page on hitting play.
Also can play 25fps instantly in the color page.

The SSD equipped machine, which hits over 600mb/s, takes close to two seconds to get to 25fps on the edit page and cannot sustain better than 15fps on the color page.

This is with all bypass selected on both machines.

Anyone have clues as to where I can look to find the bottleneck?

Thanks

I'd look at the SDI card and/or Desktop Video driver.

I had a similar issue that was eventually solved by an updated Desktop Video driver.

You could try an older or newer driver, or try removing the SDI card altogether to see if that solves it.

Yup. Its the Blackmagic HD SDI output card.
Disable it in prefs and all is well.
Turn it back on and the playback goes down the drain.

OK BlackMagic now what do I do??..Peter, are you there...??

I need simultaneous HD and UHD outputs for monitoring. I have one slot. I have a Decklink 4K Pro.

Why does the essential HD-SDI card kill my playback performance SO BADLY ????

PS I also went back one version in the video driver and it made no difference.

I'll give it a few days to be answered here and then it's to the phone.

Thanks Mark