mpig09,
You have to consider the bandwidth of the cm and the diff mode part separately. I asked you about the CM BW because I am really interested on it. I think that you should have a BW for the cm part as large as the diff BW. But I personally didn't do that to save power.
Now, about the bandwidth, you have to do two things:
* First check the predriver. Do transients to either find its BW or make sure that is large enough for your 600MHz.
* Then, take the output part of the driver (the circuit you show in the pic) and bias it in half way operation (with a zero diff signal approx). Include R and Cloads. Try to do an ac analysis on that to see the BW. I think it should be possible. If it doesn't work, you can calculate an approximation. Take the time constant formed by the 50 ohm resistor (to the ac ground) and Cload (leave that one as a parameter). consider at least 4 taus (that sounds reasonable for an lvds output) and 1/ that gives you the max freq. For 2pF it is 1.25GHz. for 5pF 500MHz, 10pF 250MHz.
You can also do it the other way around, for 600MHz, the period is 1.6ns, if you wnat to be settled in say half clock pulse, then you have 400ps to settle. The max Cload that can resit that is less than 4pF.
Just remember that Cload includes everything! Parasitics of the output transistors, the pads, bonding wires, pins, PCB traces.
BTW you can always do parametric transients while increasing the freq. That gives you the large signal BW