Code:
Plate: Ch Le Pa Ha Bp T T+SB
Evasion 138 111 83 83 83 498 553
Maximum MP 282 212 141 141 141 917 1529
Physical Def 380 302 224 224 224 1354 1578
Magic Resist 101 81 61 61 80 384 427
Physical Attack - - 12 - - 12 42
Flight Speed 10 8 - - - 18 18
Atk Speed - - - 6 - 6 6
Maximum HP 314 235 157 157 157 1020 1698
2 Pieces: +21 Magic Resist,+66 Physical Def,+27 Evasion
3 Pieces: +312 Maximum HP,+282 Maximum MP,+42 Physical Def,+12 Physical Attack
4 Pieces: +22 Magic Resist,+67 Physical Def,+28 Evasion
5 Pieces: +366 Maximum HP,+330 Maximum MP,+49 Physical Def,+18 Physical Attack
Full Set: +22% Speed,+42 Flight Time,+286 Parry
Code:
Leather: Ch Le Pa Ha Bp T T+SB
Evasion 216 172 126 126 126 766 892
Maximum MP 282 212 141 141 141 917 1529
Physical Def 226 181 136 136 136 815 1128
Magic Resist 113 91 68 68 87 427 474
Physical Attack - - 12 - - 12 12
Flight Speed 10 8 - - - 18 18
Atk Speed - - - 6 - 6 6
Maximum HP 314 235 157 157 157 1020 1698
Crit - - - - - - 120
2 Pieces: +24 Magic Resist,+45 Physical Def,+27 Evasion
3 Pieces: +312 Maximum HP,+282 Maximum MP,+33 Evasion,+48 Physical Crit
4 Pieces: +23 Magic Resist,+45 Physical Def,+28 Evasion
5 Pieces: +366 Maximum HP,+330 Maximum MP,+38 Evasion,+72 Physical Crit
Full Set: +22% Speed,+42 Flight Time,+223 Physical Def
Side by side comparison...
HP: Even.
MP: Even.
Defense: Plate by 450.
Magic Resist: Leather by 47
Evasion: Leather by 339.
Attack: Plate by 30.
Crit: Leather by 120.
So, if you went Leather, you'd need to put 6 stone slots into +5 Attack to match Plate. If you went Plate, you'd need to use 8 +15 Crit stone slots to match Leather's crit. If you consider the defense loss as taking an added 45 damage a hit, I personally can't say Leather is worth it since it's unlikely the added Evasion will really up us, either.
Then again, I'm not sure if in the set bonuses, like +12 and +18 Attack become 30, or if it just goes from +12 to +18. So, that could screw up my numbers if the latter.