Careful with the PR statistics there...
Don't believe everything you're being told.
The polygons most graphic card builders are boosting about are not the ones you end up seeing in a game. To start with those are theoretical bandwidth numbers, where as real life test benches show a lot lower numbers.
A game needs to do a lot more then just spitting polygons, so it turns out that a CPU still is one of the most important factors.
EA set their polygon standard (per object) that low, because they wanted to keep the min. config. system specs as low as possible, so they can maximize their sales.
The game however can take a bit more if you use a modern PC (P4), although you still need to evaluate how many units you want to build...
a few units of 1000 polygons is ok, but if you start making 25 or 50 of them, even your fast system will go on its knees...
My rule is to be so efficient as possible in polygon modelling, without compromising the silhouette of your model.
added:
small remark about the number of tanks you think you can keep rolling : You need at least 30fps to be playable, so start by deviding the 113m by 30...
