Jeff, I have a simialr shop and a 3hp Powermatic two bagger. I have 6" pipe that services a 20" 10hp planer, a 16" jointer, a 15" planer, Bandsaw and unisaw ( soon to be slider). I have about 25' of 6" and 6~8' of flex going to the 20" planer similar to the joiner it with a 6' hard drop then to 6' flex.
My dc supplies about 1900cfm. I don't get the full capacity because I am only running 6". Depending on species,grain orientation , and cut depth ( or feed rate) I get some the pock marks from reciculating chips on board faces in the planer. Simply the DC is not sucking out fast enough.
The reason why your system is not working starts with your hose size 4" hose will only allow about 300cfm thru the pipe. Your planer needs about 600~800cfm work at it's best. Better is to run 6" to the gate then reduce.
Dust collection is a vast subject but can still be a simple as some rules of thumb and a dc with a big impeller and good sized motor.
Clean filtration bags are a must. I have American Filter Fabric bags but unsure if I would buy again. They clog after a couple months in my one man shop with no wide belt sander.
I too live in an area where the lumber is predominantly sold rough and green. I can buy dried and skip planed but it's not really flat and not really dry and hard to straighten out a cupped or warped board that's already 13/16. So here, we all mill our own lumber in house unless it's order from the mainland. Many woodworkers prefer to work the local wood.
The Felder Owners Group on Yahoo Groups is a good place to lerk as they have very incitefull discussions on dust collection, mods to machinery and Bill Pentz posts there often on DC discussions. I think he designed the Clear Vue System.
Simple things to avoid is long runs of flex hose, undersized pipe and hose, clogged bags, 90 degree quick turns, leaky gates, long vertical drops.
The clear vue system uses a 15" impeller designed for 6" pipe and reportedly works great in small shops of about 1200sq'.
Since your using a dedicated bagger with the 10' hose I would say the bags are clogged and the 4" flex is working against you.
Most 15" four post planers come with the 5" port. I run about 25' of 6" S&D to a vertical drop then reduce to 5" with 4~5' 5" flex.
Best, Correy
p.s. it's o.k. to mill your own lumber, but geez man the 15" is painfully slow. I picked up a 20" 10hp used euro thicknesser for the same as a new 20" Powermatic and it can take off 3/8" in a single pass. The Powermatic is like 1/16" right? The biggest jump in efficiency is realizing that you can then get two 8" boards through at once. It's hard to keep up by yourself. The larger thicknesser paid for itself right quick. It also has a tersa head so knife change out is about 2 minutes. I still keep the 15" Delta around since I had put in the Byrd head the year before. Nice to have both. But I don't use the Delta unless I have some seriously gnarly grain or super hard that needs the carbide.