hmmm... well I've experimented with this a lot: Finibars pre-workout, no Finibars pre-workout, oatmeal in my pre-workout meal, SWF peri-workout, or just MAG-10/Anaconda peri-workout. However I always have rice or potatoes in my post-workout meal (~60 mins after) because it just feels right.
Anyways, mentally and physically, I always feel better with just plain old SWF during my workout, 2 scoops worth (64g). If I have a Finibar prior to my workout, I tend to have less mental clarity (kind of like a 'fog'), and I think there is definitely truth to where a big insulin spike prior to the workout messes with the neurotransmitters such as acetyl-choline. This is regardless of the type of workout I'm doing... whether it's Thib's Indigo workouts, or just straight Olympic lifting, I tend to have less focus and less explosiveness when I have a Finibar pre-workout. I've had enough experiences with this in workouts that I know it's not just 'placebo' or whatever.
HOWEVER, I do agree with having insulin increased DURING a workout because insulin can shuttle glucose and aminos the muscle. That's why I prefer to sip SWF fuel throughout my workouts, I feel like I get the best of both worlds (mental clarity and a gradual/sustained increase in insulin).
BTW in my pre-workout meal (breakfast), I am totally Poliquin about it: meat, nuts, and berries. This always works wonders for me in getting lean and having great focus.