Forgekeep vs Forgemaster

[Mature]

What would be the difference between a fully melded ilvl170 gear + accesories+ OH Against ilvl180 gear + melded ilvl170 accessories + OH?

[Ibi]

What would be the difference between a fully melded ilvl170 gear + accesories+ OH Against ilvl180 gear + melded ilvl170 accessories + OH?

Depends on what you consider "fully melded" to be.

Given that the accessories and OH are the same in both sets, we can consider just the visible slots.

i180: 553 Craftsmanship, 524 Control, 12 CP

For i170, head, hands, legs, and feet can be capped using only Grade IV and lower materia (for 36 Craftsmanship, 328 Control, and 16 CP total from the four slots). CP on the main hand can be capped using a single CP IV (I don't know if that's the most efficient way to meld, but let's assume we do that for simplicity), and the body cannot have additional CP melded.

Assuming infinite gil and endless materia supplies...

Grade V, Control > Craftsmanship: 568 (+15) Craftsmanship, 572 (+48) Control, 24 (+12) CP
Grade V, Craftsmanship > Control: 602 (+49) Craftsmanship, 546 (+22) Control, 24 (+12) CP

No Grade V, Control > Craftsmanship: 536 (-17) Craftsmanship, 567 (+43) Control, 24 (+12) CP
No Grade V, Craftsmanship > Control: 578 (+25) Craftsmanship, 539 (+15) Control, 24 (+12) CP

[PirateCat]

What would be the difference between a fully melded ilvl170 gear + accesories+ OH Against ilvl180 gear + melded ilvl170 accessories + OH?

The exact stat differences will vary because it isn't possible to cap the stats on the mainhand or body pieces. But if you start from a baseline of maxing out the pieces that can be max melded (head, hands, legs, and feet slots) with no melds on MH or body, the i170 set has -9 craftsmanship, +15 control, and +8 CP over the i180 set. Making up for the craftsmanship on the MH and body is trivial since you have three free slots to work with, and then it's a matter of which stats you want to focus on with the other melds.

That being said, I'd personally recommend saving the MH for last if you're melding or just going with the i180 version. The best you can do without overmelding tier 5 materia only barely beats out the i180 stats. (Crafts V + Crafts IV + Control IV x 2 + CP IV is all of 2 craftsmanship and 4 CP better than the i180, for example.)