George, A couple of questions...
#1 are these goals that you should go after or are you wanting to discuss what goals might be for the general backpacking population that would want to try to get to sub 5?
#2 what is comfortable weather? a kit that can handle below freezing with rain or sleet?
#3 is this meant to handle all approaches...i.e. poncho tarp, tarp, others? because I have found that the goals should change slightly depending on the approach.
If I assume this is general goals. I would encourage the use of these assuming non cuben gear because you can certainly do SUL without cuben gear and the cost differential is significant. I would not want have goals that can only be reached with a $250 tarp when a $50 tarp will work just fine.
On weather...I will assume 30 degree nights with a kit that can handle solid rain.
Next I would suggest taking another look at Chapter 15 LWB&C, Ryan suggests weights for items in a sub5 kit. I have read this chapter at least 30 times.
Given the above background here are my comments. First I would convert target to ounces to provide additional granularity, but I will stick to lbs for now realizing any one of the big 3 might be +- 2 oz.
Pack - 1/2 lb agreed this is a Murmur - $90 (7.9 oz)
Bag - I would suggest 1 lb - this would be a Katabatic Palaside or Arc Ghost
Pad - 4 oz - trimmed 3/8" CCF
Shelter - 1 lb - 8 oz tarp (NON cuben), 2 oz stakes and line, 6 oz bivy
Total is 2.75 lbs.
Cook kit - 1/4 lb - ti cup, ti spoon, cat can stove, foil wind screen, foil lid (if cooking kit contains water purification, water carriers, and lighter then yes go with 1/2 lb)
This leave - 2 lbs for everything else
The biggest concern I have with your goal is in the remaining gear. I would suggest that 1.25 lbs is not enough to have proper safety items, hygene items, and extra clothing.
Extra clothing -
If not using a poncho tarp....
fleece cap - 1.5 oz
fleece glove - 1.5 oz
puffy jacket - 8 oz
extra stocks - 2 oz
rain gear - 11 oz (anything less means goals require poncho, non durable rain gear, or no rain paints)
this is 1.5 lbs, if you are using a poncho tarp then the above list can swap out the 11 oz rain gear for a 3 oz wind shirt, but now the goals only work for people who are skilled in poncho tarping and you should probably add in 2 oz to the shelter weight target.
If I have done my math right 2.75 + 1/4 + 1.5 lbs leaves a round 1/2 lb for light, fire, whistle, compass, cutting device, first aid kit, hygene items, deet, sun screen, water purification, water carriers, bear hang kit, etc (1/2 lb will be cutting it close).
For what it is worth my suggested goals aren't just theories, I have tested and practiced these goals using items that are not made of cuben. Yes I own cuben and think it is great I'd just wouldn't set goals in general that can only be achieved with limited approaches or limited budgets.