I made a setup with crysis: 28 units moving + some more tanks just standing there as i was running out of space on the spot i chose. Remember that this is a FPS engine and is not designed for a view like this. At ground level i got steady 60fps at my test scenario.
Then i opened spring, spawned some 30 bulldogs and made em move and measured the fps. Remember that this is a RTS engine.
I will let the pictures speak for themselves.

Crysis
14 tanks, 3 cars, 11 hovercrafts moving with AI + 22 tanks onscreen standing standing still. FPS = 37

Spring
29 tanks moving FPS = 44
And as a last image here is what crysis looked when you zoom up-close:
