cyrusthegreat:1. Suppose two sets of irons have different distances, but otherwise the same stats (spin, precision, forgiveness, meter). For example, say the 3 iron of set A is the same distance as the 4 iron of set B. Is there any difference between those two clubs in terms of flight, behavior on the green, etc.?
The answer would depend in part on the Trajectory rating of each iron set. Assuming both iron sets have the same Trajectory rating (e.g. High or Med/High), a ball hit with the 4 iron of set B in your example will fly higher, land softer, and roll out less than the same ball hit with the 3 iron of set A, because a 4 iron has more loft than a 3 iron.
cyrusthegreat: 2. How about between two irons in the same set? Is there any difference between hitting a 135-yard club at 100% and hitting a 150-yard club at 90%?
Same answer as above. The 135-yard club (9 iron) will have more loft than the 150-yard club (8 iron), so the ball will fly higher, land softer, and roll out less.
But, bear in mind that a 135-yard iron hit at 100% very likely won't go the same distance as a 150-yard iron hit at 90%. The distance a particular club & ball combination will go is not linear based on the power %. In other words, you can't assume that a 150-yard club hit at 90% power will go 135 yards just because 90% of 150 is 135. This is why it's important to map your clubs.