I know it depends on how you pack.  I have done a ton of ultra light mountaineering with small packs and minimal gear.  I usually need about 4000 cubes, but we are talking about different things here.  (Lots of climbing gear I won't have to fit in a 3 DAP)

The reason I ask the question is I see a lot of 3 DAPs that have extra pouches all over them.  Is this because these packs are a little small for 3 days, or is it that these guys are going a little heavy?

I know how to pack minimally.  When I fought fire on a Hot Shot crew we would do 48 hours with our other fire gear and do it out of a buttpack.  

I am trying to figure out if I need a 3 DAP or if they run a little small if I should go slightly bigger.  I am thinking more and more of a Lightfighter Raid.

Size is subjective to your needs and environment, just as you stated.

Personally, I've got a LF/Eagle RAID that is covered with pouches.  I didn't really need to add any volume to the pack, but I like the ability to quickly get to all of the small items I may need on the move without having to open my pack and dig around.  For example, I've got rain gear, socks, first aid supplies, lights, batteries, and other small stuff in the pouches.

I agree with double_r76.

Small pouches are nice to place the more commonly used items in. First aid kit, rain gear, batteries, GPS, power bars, etc.

If I don't have to open my pack every single time I need something - well, that's a good thing.

Av.