Sounds like my setup......
That is basically what I am using, Antek multi voltage power supply, CNC4PC C11G breakout board, Three G320's, The AMT encoders( WHICH ARE AWESOME), And some Keling INc. 1125 oz inch motors. Mine is very powerful with this setup and has worked well despite my hamfisted attempts at blowing stuff up and crashing things into other immovable things it continues to amaze. I get some decent rapids( I actually turn it down to be a little safer) and there is more than enough power on tap to break endmills without a seconds thought. I did manage to blow up two geckos along the way but that is my inexperience talking and not any fault of the setup. I do not see how you can go wrong with this.....
You will really love the servos, they are amazing and nearly silent in operation, and once I got my steps per right I am getting some very accurate results for a homebuilt machine. I do recommend a slightly higher ratio for the Z axis and when you are in there make every effort to lock down the Z axis slide to the ballscrew mount. I did the mods that IH recommends and even went a little further, you can see what I did on my build thread. There is some difficulty getting the Z tight due to it's weight and I used a 3/4 inch ballscrew on the Z just to be sure. I used 5/8 inch screws on the X and Y and they are more than adequate for the size of this machine. When you make the Z top motor mount make sure you leave enough meat below the angular contact bearings to take the constant lifting of that heavy head. I chose to make all of my mount plates from 3/4 inch aluminum and the bearing pockets are not that deep so no worries.... The funny thing is none of this is hard to do but if you do not get all of it right you will be chasing little fidgety bull**** forever..... Do it right the first time and take your time. Also I HIGHLY recommend doing the one shot oiler setup with at least a manual pump. It makes a world of difference in the operation of the machine and allows you to run your gibs a little tighter.
If you are gonna run flood coolant like me I took a page from the IH setup with running the wiring inside surgical tubing and route everything with brass hose barbs. This is a real good idea and makes another little thing less of a worry, chafing on the wires from the machine running back and forth constantly is much improved. Another thing I recommend is take the time to finish your limits and homes if you intend to use them before you start running the machine, if I did that I would not have burnt out that gecko. I understand you already have a cnc mill so that may not really apply to you depending on your confidence level.
These are wonderful machines and at this size capable of some real metal removal. You will be pleasantly surprised for sure..... Good luck and if I can help you don't hesitate to ask.... peace
Pete