A modular PSU is nice for cramped cases where you have no room to cram in your unused cables. Do you need one? That's your call. Btw, I have built a variety of computers over the years and used a variety of PSUs. I like PSUs from Antec or Seasonic. The Cooler Master PSUs and even the OCZs seem to get a bad rep around here, but I have no personal experience with either.
But modular is totally your call based on your rig. It helps airflow to keep unnecessary cables out of the case, so generally speaking people vastly prefer modular. With your Antec lanboy case with all those fans and airflow, it probably wouldn't make much difference in cooling. But it'd be cleaner and overall more ideal to go with a modular PSU. Like I said, I usually recommend Antec or Seasonic.
For only a little bit more, the OCZ ZT 750 is a much better pick than the Cooler Master GX 750(its failed several reviews, there is a newer revision of it but newegg is still selling the old fail).
You never really 'need' a modular PSU, its useful if you are big into cable management and want to minimize the clutter in your case, but if you don't have a window and aren't OCD about the unseeable insides of your case modular isn't necessary but can be nicer for routing the cables for initial setup..
Personally, I'm not sold on the modular PSU concept. In the first place, all of the MB cables will be used and probably at least 2 of the SATA power cables. Then you will probably use at least 1 ea. 2x6 pin GPU cables and maybe a 12V molex cable or 2. That leaves how many cables you would have had to hide? Hardly worth it IMHO. That's a nice price for a 750W Bronze PSU though.