One of the silliest things about the forum rules is the attempt to specify a number for the "speed of thought", whatever that means. IMO the whole topic makes no sense.
If speed of thought is measured in terms of the speed of neuron impulses then it should be sub-C by definition, but obviously that changes in comics, where it varies wildly between characters. A character who has super-C reactions has to have super-C speed of thought, for instance. And telepaths/telekinetics are often treated as gaining incredibly fast speed of thought once they reach a certain tier (see God Cable somehow conducting fine atomic manipulation while fighting Surfer at super speed around the globe). I'm sure there are a ton of other examples of common scenarios affecting that sort of internal 'speed of thought'.
On the other hand, comics also use "speed of thought" in a more metaphysical sense, to talk about the speed at which a thought races from a person's brain to the place that the person is targeting... like Xavier casting his mind across star systems or Magik being able to instantly create a portal to the moon. Depending on the scenario, this speed is either actually instantaneous or there is some sort of delay between thought and effect but the process is still much faster than C, because of comic book science.
Either category makes a very stupid metric to measure Flash's speed. The first is so subjective because we are more than aware that comic book characters vary wildly in their thinking speeds. The second category is so vague it almost isn't worth discussing, IMO, except that it gets brought up in confusing narration all the time.
In all likelihood:
If Flash were in position X when Invisible Woman completed a thought to wrap X in a forcefield, I think Flash would get wrapped in a forcefield (he's just vibrate through, but whatever). Pulling this off would require either attacking Flash unawares, incredible luck, or some almost PIS-level planning and anticipation (see Deathstroke stabbing Flash).
On the other hand, if Flash were in position X when Invisible Woman initially reacted and started forming the thought to create a forcefield, Flash should/would be long gone by the time the forcefield appeared.
