Never tried a 3.0 but have sprayed with a 2.5 it into a mold using a cup gun but it couldn't get more than half a liter sprayed before starting to gel in the cup. It did lay a little down a little smoother than my dumpgun and would be a better suited for small repairs than a dump gun.
I also have a cheap gravity fed gun w/ a 2.5 & 3.0 tip I use to spray clear topcoat into molds. It's viscosity is a little lighter than gelcoat and doesn't gel as fast as gelcoat but puts it out it out nicely. Got the gun off ebay or Amazon for about 45.
Didnt really answer your question but all that's all the experience I have spraying gelcoat.
I have a cup gun but I don't like the work it does. Too much orange peel with a 4.0 tip when a HVLP gun is not that hard to clean. For mold work I thin the gelcoat 8% with styrene and for finishing work I mix it 5:1 with patch booster. I cool the gelcoat ahead of time in ice so down into the 60s and I use a cooler for my compressor so the air doesn't cause it to gel early and clog the tip. Working 15oz (18 after patch booster) at a time with 1.5% MEKP is not an issue for me. I can do 10oz at a time if I don't cool anything. This is at about 90* ambient. However I have to clean the gun every batch.
It's not too bad I just put acetone in the gun, brush it, dup that out, then I put new acetone into the gun and let it run through into a cup. I use this dirty acetone to clean the bulk of the next batch out of the cup which saves a lot of acetone.
The 2.5 tip does give me good results and enough build up for sanding at 150 with a DA. I do things a bit differently but basically the same on the last coat.
Also note that I say mold work and finishing work but the quantity of projects I have done is very few and my work is not to the level I would like it to be. You probably have better results than I do and am just saying what I do for the sake of conversation.