I tried using 3DSMax but the .stl file ended up being 5GB (from 80mb). Are .stl files so poorly optimized, or is there a better alternative?
Its not about optimization but totally different representation of geometry. IGES files describe parametric surfaces that must be “baked” to polygon surfaces. Depending on set conversion detail level it can produce gazillions of polygons, which is why converted file is huge.
You can test different comversion settings or find someone (or do it yourself) to clean up the geometry first and possibly convert different parts with different settings for optimal result. Occasionally I have had to deal with IGES files and I let my friend to the conversion for me. He uses Rhino3D for this work and it has usually involved some manual fiddling with geometry to get good results.
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Best conversion tool I ever found is Moi3D. I get cleaner meshes than Rhino.
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That’s a bit off topic, but just in cases you run out of solutions this may come to help :
On one project I add to import a IGES file , converted to VRML . The .vrml file was 80mb and it crashed blender.
I’ve had to hack a bit the vrml importer script so it import just a part of the file into blender, like from 0 to 100 objects, then 101 to 200 ect… Like this I managed to import the whole file in chunks.
At that time we’ve tried to import the .vrml into maya and meshlab and both crashed , only Catia (from which the .vrml was exported from) handled it successfully.
From what I remember it was the last project I did with 2.49 so it was long ago 
Good luck !