3 of the 4 I500 iron sets don't really make a lot of sense.
The distances of the 3 are almost identical. All 3 are high trajectory. the top 2 sets have the same 4.0 precision and the lower on is only .5 less. all 3 have 3.0 spin. the biggest difference in performance is forgiveness which is 3.0 for the level 83,2.0 for the level 69 and 2.5 for the level 59. Meter speed is 3.5 for the level 83 2.5 for the level 69 and 4.0 for the level 59.
What really makes no sense is that the level 69 set is 200 credits cheaper than the level 59. If some one can handle the faster meter speed of the level 69 set it would be the one to buy.