Regarding the Silshelter: I never saw anything particularly wrong with it; I used it a number of times with a bivy, and was really quite pleased. (Well, except for that one moment that I accidentally kicked over the pole that was inside, holding the foot end up. A little cursing and grumbling, and things were just fine.) I only quit using my Silshelter-and-Salathe system when they finally came out with a tent that was equally light and versatile (the Hubba.)

As far as clothes, you bring up a valid point: you don't want to wear bulky clothes inside a tight-fitting bag. If you do, you just end up compressing all that down, and accomplish nothing. However, if the bag has some extra room (not tons, just enough for that mostly-not-confined feeling), you can wear some light insulating garments inside. For example, my WM Megalite bag doesn't fit tight when I'm wearing my synthetic long johns. So, I can, if I need to, wear my light down sweater and pants (NOT a full, Michelin-Man style down suit!) inside the bag and gain some warmth. The weight of garments that would be appropriate for this would be something like the Montbell UL Down Inner series clothing.

Also, I don't go out intending to rely on my clothes. Since I have a 30-degree bag, I normally plan on nights no colder than 30 (or 25, since the bag's rating is conservative.) However, for those unpredictable times when the temperatures drop to 20, I know I can wear my clothes in the bag and stay warm. In effect, my safety margin is in my clothes, not in the bag itself. That works fine where I am (the Ohio Valley), where forecasts are generally reliable. I don't know whether this clothes-as-sleeping-system will translate as well where you are.