You can use any size repeat, but really small ones won't give you much variety in the blocks.
I think #1 would make a really interesting OBW.
I have #2 and have been saving it for a OBW or S&W.
#3 - not a lot of contrast, but there are some beautiful colors, I would be tempted to try it.
#4 is not very good for a OBW because of the straight lines.
#5 is similar to one I did with fabric that had dogs on it. It's interesting because you can look at the OBW and see little tongues or snouts or eyes... Not a lot of contrast, but I still like it.
#6 - I wouldn't use it because there's so little contrast.