Actually, it's not only the "presweetened" part, it's also the "instant"
part. Most pre-cooked, instant or whatever food products (rice, pasta,
oatmeal...) have *insane* GI index. In some cases, the added saccharose is
actually the low GI part of the product, since some of these actually come
close to pure glucose on the GI scale...

All of these reducing GI down to moderate/low values (and you don't have to
mix all these together, as long as they're in the same meal, it will end up
mixed in the stomach anyway). But maybe there is another element at play
too. Some nutritionists claim there is a notion of partial hungers; the body
will crave for some macro-nutriments and will continue craving if it hasn't
gotten it. Some claim there is no differentiation between carbs and fats,
since they're both energy, but there is one for proteins. That should not be
a problem usually since the body seems to be content with a daily average.
But if you're dieting, there is some chance that maybe you are borderline on
the macro-nutriments you get. Hence the added hunger if you didn't get
enough proteins/fats.

Yes, and it doesn't seem to be a question of being regular or pre-diabetic.
I'm a T2, but I lost my weight through hunger/satiety and doing lots of
experimentations with my nutritionist. This involved eating single food
meals, like French fries or chocolate only. True, I never ate pure sugar
(I'm not suicidal, besides it's not a very satisfying meal), but high carb
content didn't seem to disturb long term satiety, French fries and chocolate
worked just as well as cheese. The only noticeable difference was the kind
of energy I would feel if I exercised shortly afterwards, sugar gave some
kind of nervous energy I didn't get with fats.
Though it seems I can't do this kind of tests anymore, it seems I'm now able
to survive a full featured English brunch (scones, muffins, tart, eggs...)
with a post-prandial at the same level of my fasting (1g) :)

Weirdly enough, snack did cause me a slight rebound, while meals didn't.
Though something like chocolate or fruits did fine with me, it was really
pure sugar that didn't do the job.