7:21 p.m. on February 25, 2013 (EST)
I know you asked for info on sleeping bags, but have you thought about using a single quilt to cover you and your wife? The advantages of a couple sharing a sleep system are so significant that I feel it should be mentioned.
My wife and I currently use a Ray Way quilt my wife sewed together from a kit.
Ours has two layers of Rays "alpine" synthetic insulation for a 20 degree rating, the "draft stopper" all the way around and no zip split.
Our completed two person quilt weighs about 2-1/2 pounds, and is very warm. The only real disadvantage is you have to sew it together yourself and if you or your wife don't already sew this can be a minor challenge, not to mention you'd need a sewing machine.
A few words may be helpful if you are not familiar with sleeping quilts. They are much like a bag, but have no zipper. Instead of a zipper they are sewn up for a short distance on the bottom to make a foot pocket, and the quilt does not go under the rest of you. All your bottom insulation is provided by your sleeping pads. This makes sense if you think about it because the sleeping bag under you is so compressed by your weight that the sleeping bag under you is of little use, so why bother with it?
Here is Rays web site to check it out if you wish -
http://www.rayjardine.com/index.shtml
I think you can buy a two person quilt from several vendors if you don't wish to make one, or simply buy a big rectangular sleeping bag and use it open over the two of you.
For close to twenty years this is what my wife and I have done. Our old sleep system was the discontinued "thermanest" sleep system made by thermarest. It consists of a sheet to join two regular thermarest pads with a zipper on three sides. The top cover is provided by a single rectangular sleeping bag with a matching zipper. Here is a picture of it laid out on a recent trip -

One sleeping bag on top, two pads joined in a zippered sheet below. With the old regular R5 thermarest pads this is a remarkably warm and comfy sleeping arrangement, and is lighter, cheaper and less bulky than carrying two of everything!
The advantages of a double sleep system are many - So much so that I wonder why a couple would ever use anything else.
A double quilt or single rectangular bag is alot cheaper than two sleeping bags.
They are very warm because you get to share body warmth! The last really is such a significant advantage I wonder why all couples don't sleep together when camping, and instead sleeping together is reserved as a survival technique for people with hypothermia and extreme mountaineering. This doesn't make sense at all to me!
A quilt has no zipper to snag, jam, and break, so it is more reliable than a sleeping bag.
Why oh why carry two of something when only one will do?
When my wife and I go backpacking she carries our quilt and our two sleeping pads. She also carries our dopp kit and first aid kit. This makes for a somewhat bulky but light load.
I carry our shelter, our stove and cooking gear, and the bulk or our food.
All that is left is our rain gear ( inexpensive Dri Ducks suits that weight 10.1 ounces for the jacket and pants combined, and serve as both wind shells and rain gear, and maybe Golite 6 ounce umbrellas if we expect real precipitation ) and whatever extra insulating clothing we feel is needed for the trip.
I'm sure you know about the backpackers Big Three - The three heaviest things a backpacker carries - Shelter, sleep system, and what is often the heaviest single thing, the backpack itself.
My wife and I each carry only two of the Big Three, so we cheat! You and your wife should too.
Our frameless Golite Jam backpacks weight only two pounds, and easily handle our light loads. Since my wife doesn't have the best knees or back, this system keeps her total loads with water to less than 15 pounds, and even with food for four or five days my load usually doesn't exceed 25 pounds. My base load, that is to say without fuel, food or water, but with a tarptent not just a bare tarp as shown above, is typically 12 to 14 pounds, depending upon how cold it is.
You can do the same, making your hikes very enjoyable and saving coin at the same time.