Personally, I'd go for the saw. Chopping with a blade tends to distort surrounding material, causing more damage than a small amount of stock removal in a nice, straight line. Something has to give way to make room for that blade, after all. Razor saws aren't expensive, if you don't already have one, and have very fine and narrowly set teeth on thin plates. The kerf on even a basic one from a craft store or Amazon cheapies is still less than a millimeter.
I've just always found it easier and cleaner to saw. If 1/4 or 1/2 a millimeter makes a difference to look or fitment (it rarely does, in my experience), I just add a shim of styrene sheet (0.010" and 0.020" respectively) with plastic solvent cement and sand it to fit. Faster and less fiddly than trying to resculpt the area, since I generally plan cuts at the edge of details or on smooth shapes. I generally only break out the epoxy putty when I'm modifying more than one angle, which necessitates leaving significant gaps.
Of course, if your test pieces turned out well, there's no harm in continuing to do what you're doing. That's just the only advice I have to give and it's served me well, thus far.