Touring - HOw big is too big for a handlebar bag?

I see Nashbar has a large handle bar bag for sale. 420 cu. in.
I would get it for family rides, multi event activities and touring.

I especially like the map compartment on top.

http://www.nashbar.com/nashbar_photos/medium/NA-HBE.gif
http://www.nashbar.com/profile_moreimages.cfm?category=66&subcategory=1002&sku=16797&brand=

Does anyone have any input on this type of handlebar bag?

IMHO, it isn't the size, but the weight of a bar bag that I want limited. The exception to this rule might be in VERY windy conditions, where the aerodynamics of the bag might affect steering. I particularly dislike any weight high in front that makes the wheel want to "flop" from side to side. Low-riding front panniers on a front rack are one way to avoid floppy steering, so I've heard (never tried them yet). I'd probably avoid the large bag only because if it were there, I'd "load it up" and get into the steering problems I want to avoid. Your preferences may vary.

For larger loads, a big saddlebag makes more sense.

I'd get the smallest bar bag you can, just something that takes the maps, the camera, the money and the shades. put everything else on the back.

The bigger and heavier the bar bag, the more annoying it gets as every time you stop the bike falls over

I use a road bike so I can't have anything but the smallest available bag because it'll hit my tires.

http://bikemart.com/images/library/large/jandd_mtnhndlepck4_03_m.jpg

This one is big enough for my sunglasses case, keys, wallet, cell phone, mp3, digital camera, snacks etc, plus it has a map case that can be flipped up to view, or tucked away. I wouldn't want to put anything more into it because of the weight, so this works well. (I even got a miniDV video camera in there) Also fits between brifters easily.

I use an Ortlieb front handlebar bag mounted under my aero bars, just to keep, sunnies, wallet, medications, and phone in. Everything else is behind me. I found this type of bag has a reasonably small wind profile compared to others, keeps the weight down (limits what you can get in it) and is waterproof.

I also use a tri bag for lip balm UV protector and sun cream.

I see Nashbar has a large handle bar bag for sale. 420 cu. in.
I would get it for family rides, multi event activities and touring.

I especially like the map compartment on top.

Does anyone have any input on this type of handlebar bag?
What I don't like is that they don't show the mounting bracket. I got the Performance tour bag and it has nice metal C-clamps but a plastic plate the bag rides on. It's OK but I don't know about a long haul.