I had a 8gal surge tank on my 80gal reef tank for 13 months and it was pretty strong. The factors that I can see that determines the surge strength is the exhaust pipe diameter, the total volume in the surge tank, in my case 8gallons, and how fast the surge tanks fill up.
You might want to try several smaller ones throughout the tank rather than one or two large ones in hopes that they will cover everything; but in your case "small" is big for the rest of us.
Another thing is that you may want to set it up so that the surge exhausts are not too close to the rocks or have them blow through mini canyons that you created with your rock
_____canyon wall
- - -> surge flow head on view: \*/
_____canyon wall
To get a decent flow if your only going to use surge devices, I would recommend that the total sum of surge volumes be 8-10% of your tank voulme (mine was 8gal on a 80gal tank, so it was 10%). You can go lower of course since this may be difficult with such a large tank, but the closer to these values, the better off you will be. Just my educated opinion. :reading: