Since you asked...
For years I used gravity feed HVLP cup guns. But, I got tired of refilling the cup over and over. For a lot of my projects, a single part would require spraying more than half of the cup's capacity. So, I would fill up the cup after every part. (Some of the larger parts are 32" x 82" or bigger.)
Earlier this year I purchased a number of pressure pot systems and HVLP guns. I have separate systems for water-borne and solvent-based products. I don't want the hassle of the change-over and cleaning process between types of products. I even have a separate system for spraying dyes (think color stains) since it uses a different solvent. I also keep primer and topcoat in separate systems. That's nice when I am spraying lots of parts (maybe 30-50?) and want to do them in batches. I don't have to change the gun over from one product to the other then back again. Time is $$$. For some of the products I can leave them in the system, under pressure, for days or longer.
Anyway, I bought 2.5 gallon pressure pots and HVLP spray guns. I do not pour the finish material (lacquer, primer, etc.) into the pot. I simply place the entire gallon container in the pot. The pickup tube fits very well and will get almost all of the material out of the gallon can. It may leave a 1/2" or so.
I find the pressure pot systems to be much faster than the gravity guns. I can control how much fluid comes out by adjusting the air pressure pushing into the pot (which then pushes the fluid through the fluid hose to the gun) as well as adjusting the needle travel (as with your guns). I can adjust the air pressure for atomization with a separate air regulator. There are two regulators on top of the pressure pot.
I can keep spraying without the need to refill for quite some time now. I can also hold the gun upright, sideways, even upside down. I can reach over the parts and easily spray the opposite edge by aiming the gun back towards me. (Yes, I wear old shoes and clothes. The exhaust fan catches/pulls most of the overspray away from me, but some still gets through.)
The HVLP guns have been shown to be more efficient. There is less overspray. Well, the operator must adjust everything properly of course. But, you do not need as much air pressure to get good atomization and a good spray job. As you know, needle/nozzle size is important. For my primers I use a larger nozzle size than for the finish coat, just like you do. The primers are usually thicker.
The photo is one of my setups. The airline from the compressor is on the right. The yellow line is air to the gun. The white line is fluid to the gun. The right regulator controls the pressure inside the pot, which then controls the fluid pressure to the gun. The left regulator controls the air pressure to the gun. The gun works pretty much like what you are using. There is an adjustment for fan width and nozzle opening on the gun just like yours.
It's nice not to have the extra weight of the cup and fluid at the gun. And, being able to spray an entire gallon before a refill is needed. Holding the gun at various angles with ease is a bonus.
OK. I'm wearing my fingers out here.