فَأَمْرِي صَبْرٌ جَمِيلٌ
My course is beautiful patience.
This reading begins with the speaker's own course of action («أَمْرِي») and identifies it as patience: the statement tells us what the speaker has chosen.
فَصَبْرٌ جَمِيلٌ أَجْمَلُ بِي
Beautiful patience is more becoming for me.
This reading starts with beautiful patience and judges it to be fitting. The practical outcome is closely related, but the focus of predication differs.
Economy allows these two plausible shades of meaning to coexist. The range of meaning is not unlimited: each reading needs a sound syntactic structure and a connection with the occasion.