There's still some optimization to be had, but not much without losing a lot of quality.
About quality, you need to think "final" product... i don't know if you segment/UV/texture yourself your models but some details can be made via texture work...
by example, you have a lot of gun with numerous barrels... it is possible to make the "inside" of barrels via normal map... will spare only a few poly by barrel by since the huge amount of gun/barrels...
Or on both side, at the back of the model, you have a trench with panel... for the smallest one, it is possible to make it via texture too...
Anyway, your models are great... if they don't make it in sins due to poly limit, maybe they will make it in sins 2 !!!
Or maybe you have a early version with fewer poly... i don't know how you work but in my case, i always start with a "3D sketch" who is low poly ( 1 or 2k poly )... by example, take a look for the sharlin that i have made for the B5 mod... http://3.bp.blogspot.com/_EpX6GUNLABE/SrbZuvscp0I/AAAAAAAAAME/pnOM-Of7G8g/s1600-h/sharlin.jpg ... fight model on the left, second stage on the right... one more stage at http://4.bp.blogspot.com/_EpX6GUNLABE/StnQ4zOdABI/AAAAAAAAAV8/cdTuJlgy0hM/s1600-h/sharlin_11.5k_tri.jpg ... in game result at http://babylon5ins.blogspot.com/2010/04/b5-s0tyr-sharlintex-update.html ... as you can see the texture work from Tobi and Steiner have greatly improve the details of my model...
In short, if you have somebody who texture your models, it is a good idea to ask your texturer about what details can be made via texture work... it will allow to optimize the model without loss of quality in the final result...