After hours of research both here and elsewhere on the internet, I find myself with questions not necessarily addressed in other threads.

I'm looking at the REI Minimalist Bivy combined with the Lafuma +45 deg. bag for summer in the big mountains of the Northeast (ADK, Whites, etc). I already own a Cocoon silk liner adding 5-10 deg. more warmth. So, my "combined rating" should be around 30-35 deg., perfect for most summer nights in the mountains, and hopefully, by using a 45 deg bag with the liner and my clothing, I give myself options to help prevent overheating and thus condensation. Here are my questions

#1. Are bivy's, and specifically the REI Minimalist, really truly waterproof? As in, could I lay out in a teeming rain with no tarp and not get wet (other than condensation, which is question #2)? I understand the REI bivy has a mesh face opening, which I'll easily seal up by rigging my poncho over my photo tripod and placing that over my head. But other than that, is it the real deal as far as waterproof goes?

#2. To battle condensation, I figure on the Lafuma 45 deg. bag with the silk liner (making it a ~40 deg. bag). I'm a fan of bringing more clothing and thus a lighter sleeping bag. I'd rather have clothing that I can move in to keep me warm than a heavier bag that keeps me immobile. So if it gets chilly, I add my fleece and if it gets real cold, fleece lined soft shell plus boiling water in a nalgene. However, I've heard bad things on Lafuma's loft, so maybe I should stick with the Lafuma 30 deg. bag I have now? I'm just worried about overheating and condensation. I know some is inevitable when using a bivy, I just want to minimize it through intelligent planning

If I pull this off, I save something like three pounds. Three entirely beautiful pounds, gone from my pack forever! Not to mention the ease of use and setup, real handy for a photographer who routinely rolls into camp well past the glorious hours of sunset. I'm not concerned with any other aspects of the bivy as I am Spartan camper, and my daylight hours in the woods are always spent hiking, rain or shine, since I only get to get out so often in a year that I make the most of each and every day spent on the trail!

Thoughts on this idea, or any others?

Here are links to both the REI Minimalist Bivy and the Lafuma 45 deg. bag.

Bivy http://www.rei.com/product/794292
Sleeping Bag http://www.rei.com/product/798906

Thanks everyone!