I'm totaly lost with spiritbound... what is the best IL to convert? please

[Nutz]

I dont see how 2.3 broke the materia system. Grade IV materia shouldnt be 100%. If anything it was a welcomed change IMO

Why shouldn't tier IV materia be 100% on much more expensive equipment that takes much longer to spiritbind? It's not as though tier IV materia is or should be some ultra rare item. It's completely required to participate in high level crafting and gathering as well as necessary to make crafted combat gear relevant. It should take more time/ money/ effort than tier III materia, sure, but the current ratio is ridiculous and has had the unintended effect of drastically increasing the supply of tier III materia such that in a lot of cases it's cheaper than tier II.

Sorry, on topic. OP, I've always found that using level 45 equipment is as good as you can do. Anything 45-55 has the same chance of converting to tier IV, but 45 will SB much faster (I think about 50% faster in Urth's gift), is cheaper to produce, and easier to HQ if you're making it yourself and not a geared up crafter. Basically use the lowest ilvl equipment that you can that is 45+. This will probbaly be in the 45-50 range. To me ilvl 55 gear is just not worth it.