You're on the right track, I think, with having two identical ones. Side-by-side displays works much nicer when they both have the same vertical size, resolution and position.
You've just got to wait and see what's up with the new MacPro's graphics ports.
It would be very unreasonable, I think, if the new MPs did not work with the new LED Cinema dlsplays. But Apple has hardly been reasonable when it comes to their displays and the graphics ports their computers support.
But I'd be wary of investing too much $ into the new LED displays... the weird Mini DisplayPort connector will severly limit the computers you can use them with. Would you be happy with the possibility of replacing them in x years because they won't work with the next computer you get? If history is any guide, even Apple will abandon Mini DisplayPort after a couple of years.