1: higher rank equipment loses durability much faster than equipment with a rank similar to yours or lower. Also, of course, it requires an higher ranked crafter to repair (which means you may find yourself looking for someone that repairs it for a longer time), and costs more to repair at the NPC
2: higher rank gear scales down with level, but it doesn't scale down with perfect efficence. This means that if you're at rank 27 and wear a rank 27 armor, it will give you better stats than a rank 50 armor. The rank 50 armor will still be viable, but not as good as the one comparable to your level.