The accuracy is in the receiver, doesn't matter what display you have in the cab. So yes you can move that around machine to machine through the seasons. 

So if you want the 7000 to have better signal, easiest is the SF-RTK. No activations or anything needed on the receiver or display, just $1500/yr on the receiver subscription. And you might get a discount for the first year since you haven't had it on there yet. So more like $1k the first year. 

To run better signal on the 3000 or 6000 it'll cost more since they need the permanent activation(s) first and then subscription.