Ultralight from scratch, not practical.

You can get a 1 pound 20 degree bag. It might cost more than either of your two choices, but you won't find yourself down the line wanting to save a pound and having to buy a new bag.

I think the trouble is that people new to this sport go to REI or read Backpacker and think these are the only and the best choices. They also think that ultralight stuff is really super fragile. I hiked the PCT and my gear is still perfectly good. How many weekenders with their bombproof stuff have hiked 180 days yet with it? It takes a long time at a weekend here and there to even get close to wearing stuff out. The exception may be young boys.

The other problem is that we have all been VERY well trained by our culture that any time you want to take up a new activity you have to research and buy a whole bunch of stuff. Lots of gear can come from thrift stores, recycle bins, your closet or your garage. You don't need the best of everything. Lots of crappy stuff is light and works just as well as "the best." Do your research here or on thru-hiker-oriented web sites, not on sites where they sell the gear. Then you'll see how easy it can be.

Sadly we're such a stupid lot we will actually go shopping to find "barefoot shoes" when we were born with them. You have to fight this tendency.

It's a misconception that Southern California doesn't get cold. It gets real cold. Many PCT hikers are shocked that most of their coldest nights were in So Cal. A 20 degree bag is barely enough for me during the seasons I like to go backpacking the most. It's usually below freezing.

Yeah, again, false economy (and illogical).

20F bag – 2 lbs – $180.
45F bag – 1 lb. – $160.

First off, combined total is $340, not $240.

Secondly, much depends on where you camp (as stated by others). For summer use in So Cal — it would be silly to buy an on overly warm 20F bag just because it's not that much more expensive than what might be a more appropriate 45F bag.

Using your logic, you will also end up buying a larger backpack than you need just because it doesn't cost all that much more than a smaller pack.

And at the end, you will end up with overbuilt, oversized, and overheated gear — because they all seem to be "more bang for the buck"! Illogical and counterproductive though.

Piper, agreed but I think its fair to say for most* beginner* campers in So Cal a 32 degree bag for summer time use is just fine.

False.

The REI "So you're interested in backpacking, eh?" special:
$240 Osprey Atmos
$85 REI Polar Pod 25 Degree (really 35 degree)
$200 REI Quarter Dome T1 Tent
$40 Thermarest Zlite
$25 Princeton Tec Headlamp
$20 Nalgene Bottles x2
$65 Katadyn Hiker Filter
$40 MSR Pocket Rocket
$10 Aluminum pot
$70 REI "El Cheapo" Traverse Trekking Poles

Total $795

UL:
$125 Golite Jam
$250 Marmot Arroyo 30 degree
$200 Tarptent Contrail
$32 Gossamer Gear Nightlite
$25 Princeton Tec Headlamp
$20 Platypus x2
$8 Aqua Mira
$35 Caldera Cone
$5 KMart grease pot
$80 BPL Stix

Total: $782

QED

It does get real hot at lower elevations in summer so I never go backpacking during summer. I wait for about Thanksgiving weekend and pretty much only backpack between then and May. Sometimes June if I can stand the flies. Might do an August trip in the San Jacintos. For then, I would think a 32 bag would be enough.

Having a 20 degree Golight Ultra quilt, I've found that if I'm too hot, I just drape it loosely over just one piece of me. I have felt that my quilt has been an excellent choice for me. I only keep my old 3lb zero degree dinosaur just in case the oil crash hits and we're all plunged into anarchy or some other such disaster occurs.

Piper:

The point isn't whether a 20F bag is too cold or too hot for you or anyone else. What people disagree about with OP is just how sweeping his POV re. "economics vs. weight". There are just so many different factors at play out there.

Yeah, and my point is that he can have the warmer of his two options at a lower weight than either of his two sleeping bag choices. And the only suffering he'd have to do is being too hot during those few hot summer months.

"the only suffering he'd have to do is being too hot during those few hot summer months."

Even that is not necessarily true. If using a quilt or full zip mummy, both can be used fully opened to keep cool in warm weather.

I like the looks of the Katabatic Sawatch. 22oz for a 15F bag. It's pricey, but will work all year round and is very light!

Just what I was about to say, Lynn!

'Cause I think this troll has been fed enough.