It depends on what looks good. Depends on how fancy or plain the beads are, how fancy or plain the centers, and crucifixes are, etc.
I have a lady who makes my rosaries for me. I’ve bought beads, sent them to her, or selected from her online site. I’ve always selected centers and crucifixes from her online site. She takes pictures of my selections, and emails the pictures to me. Sometimes, it takes quite a bit to match up beads, centers and crucifixes. What you imagine, isn’t always what looks good.
I have a rosary made with 8 mm beads, a 1 inch center, and a 2 inch pardon crucifix. Anything smaller looked weird with the beads. However, I’ve seen 8 mm rosaries with 3/4 to 5/8 inch centers, and 1 5/8 inch crucifix, which looked just fine.
I have a couple rosaries— mixing 6mm Ave Maria beads, and 8 mm Pater beads. The centers are 3/4 inch and 1 5/8 inch crucifixes, and they look fine. I tried a larger crucifix, but it didn’t look good.
I have one rosary made with 4 mm beads. The center is 5/8 inch and the crucifix is 1 5/8 inch. Any larger center or crucifix— it would have looked ridiculous, since the beads are so small.
I have one rosary bought online from a rosary maker back east. The rosary has 8 mm Ave Maria Beads, and 10 mm Pater beads. The center is 5/8 inch, the crucifix is 2 1/4 inch. It’s beautiful but my least favorite rosary. Too dang heavy!
I hope this helps.