okay, an update - i think i've found the mod that's causing all the 30% crashes - still testing, but it seems this is the one: !#+
TurretFix+FasterTurretsnow, this is just one classfile, and is really still in debate as to whether this is even needed separately, as it is included with the SAS_Engines mod.
i've used this mod for some time now, without problems in the past.
however, as soon as i removed this, my missions loaded normally.
what i suspect, is that it is not the individual mod that is at fault, but more likely the way, or the order, in which some of these mods, interact.
so, between this one, the Engines mod and the Visual mod, which has a fix that needs to be loaded before the Engines mod, as indeed does this one, i think there is something breaking down if these mods are used in a certain sequence.
this is still just theory, but as i test more, i will have more facts.
i have already tested twice with this, and as soon as i put this turret fix mod back in, it crashes my missions at 30%. take it out, missions load.
so, somewhere along the way, the Engine mod, Visual mod and this AI turret fix mod, are having problems getting on with each other.
at least, this is my theory so far.
anyway, slowly rebuilding my install, and so far, so good.
sanity is slowly being restored, thank goodness. no padded cell needed for the Easter weekend, after all, lol.