I'm including both 3DSmax triangle counts and the more meaningless ObjectivII face counts:
M16A4 =============
3DSM triangles:1142
O2 faces: 635
M16A4/M203=========
3DSM triangles:1496
O2 faces: 815
M16A4+ACOG========
3DSM triangles:1378
O2 faces: 757
M4Suppressed=======
3DSM triangles:1385
O2 faces: 761
M4M203============
3DSM triangles:1664
O2 faces: 900
Note that the M4 with QD suppressor isn't a final version. It's going to get a few more details, and trade the iron sights for an Aimpoint, to make it a SOPMOD M4.
Also - these are all my working versions, no model in-game will have this much detail. I'll be deleting the areas that remain unseen from 1stPP, so I hope those counts will be around 75% of what I wrote above. The nearest 3rdPP will be the highest, close to what I have above but with the remove of some tiny details. I'll keep the LOD distances tight so that if you have a group of Marines in formation, you won't see any top level LODs.