It should work with either:
2x 1080i50
2x 1080i60
2x 1080p25
2x 1080p30

not:
2x 1080p50
2x 1080p60

There is some latency - but this depends on the spec of your MacPro.
Basically - use the best (newest) you can

Also worth considering using some SDI isolators or a local SDI-DA to avoid any card damage from external sources if you have long cable runs etc...

As always:
You must test your setup yourself as it may differ from other users scenarios and results.

S