Install Rating (3rd Party Work 10 = Best, 1 = Worse)
Short 5th gear will mean Engine doing about 800 more rpm at 70 mph than with the long 5th gear.
This therefore (can) improve fuel consumption depending on your engine output, but will reduce noise levels.
Not a job for your average diy'er but for any reasonable mechanic, not a problem. Took me 45minutes start to finish. hardest part is working out how to check the oil level afterwards!