Even at 5.5 watts you will not be happy. The problem with multiple passes is that you get more smoke damage round the edges of the cut, that's one of the reasons why people try not to do it. You will also ahve a problem with depth of field if you try to cut anything over half a mm. The depth of field of those solid state lasers is not good. You need a long focal length to get the depth of field, at least 50mm preferably more. The advantage of the blue over the IR is that you can focus it by looking, on the IR you can't because the lens bends visible and IR light differently so even if you focus with a visible laser it will not be in focus on IR.

The CO2 are a pain, needing water cooling, they crack in no time if you forget to turn the water on, they all make lots of smoke that oyu need to remove or it affects the beam path and makes the cut / engrave line wide.

My advice would be to buy a fret saw or a cnc mill.