Cards with Bestow vs. spell type triggers

[Norm4eva]

Bestow is an interesting mechanic for lots of reasons. Unlike Morph -- which turns the card face-down before it goes on the stack, so as far as the game is concerned the spell was virtually "always" a 2/2 for 3 -- Bestow doesn't actually take effect until you start paying for the spell. The choice of cost to pay -- regular casting cost, or Bestow cost -- determines whether you're casting an Enchantment Creature or an Enchantment - Aura. Up to that point, the spell is on the stack as a creature spell.  The Theros release and Tabak's further commentary are explicit in regard to this; you can control Yeva, Nature's Herald and cast a creature with Bestow whenever you could cast an instant, AND you can choose which cost you pay - so essentially they act as Auras with Flash as well.

Additionally, effects like Aurelia's Fury will not preclude you from casting Bestow creatures as Auras, because the spell went onto the stack as a creature, so Aurelia's Fury can't prevent it from going on the stack since it already *is* on the stack.

So my question is more about triggers, because while I see that triggers are checked at the end of casting a spell and before the active player receives priority, I'm unclear as to whether "Whenever you cast a creature spell..." would trigger, or "whenever you cast an Aura spell..." would trigger.

I seem to recall some older language about the way M:tG checks for triggered abilities as "the game looks back in time to see the state of the game just prior to the trigger" or some junk. This was used to explain why something like Rotlung Reanimator and a board full of Clerics would "see itself go to the graveyard" even though it wasn't in play/leaving play at the same time as all the other Clerics, and put a token into play for itself as well as the other Clerics when the opponent resolves Wrath of God. I'm uncertain if this is just a convenient way of explaining it, or if this would even apply to casting spells.

So, which effect would trigger in the event one casts a card with Bestow? Does it always see "Enchantment Creature" and nothing else, regardless of which cost you pay? Or will "Whenever you cast a [spellType] spell" triggers look at the current state of the spell on the stack?

[Clariax]

The last step of casting a spell is where abilities trigger from it being cast.  This is after it's been set whether it's a creature spell or not, so such abilities will only trigger if your choices match the trigger condition.

[Norm4eva]

The last step of casting a spell is where abilities trigger from it being cast.  This is after it's been set whether it's a creature spell or not, so such abilities will only trigger if your choices match the trigger condition.

So if I understand correctly, "cast a spell" triggers wait until everything about the spell is determined and you would regain priority? So Vengevine would never trigger from a Bestow cost being paid, is that correct?

What about an effect like Insist?