Difference between Hard castors and standard castors?
Ans: Hard Castors has a rubber coating for better grip and traction to reduce gliding from chair. Recommended for those who likes to lean back.
Headrest's difference?
Ans: Please check out:
http://deluxeforums.hardwarezone.com.sg/70237863-post461.html
Posturefit VS Lumbar pad's difference?
Ans: Posture fit can control exactly how much support with a knob, it can't go up-down and is fixed in position.
Lumbar Pad can go up-down movement but with only two length of depth for support
Is it worth to get the Polished Aluminium?
Ans: Actually the polished aluminium is not only for the better look. IMHO the Chrome Plating seems to make it harder to scratch or scratches less visible. The original Graphite frame is already very sturdy and not easily visible with scratches