How good is Ethercat motion control?

I'm looking forward to retrofit an new to me Okuma MC30-VA mill. I already have another okuma will with a Mesa setup that's been a workhorse and never skipped a beat for the last 3 years. It uses Delta ASDA A2 servos (Incremental with home switches) and it's been incredibly accurate and repeatable with properly tuned servos. Even 3D surfacing at high speed, it handles like a champ.

So I need to use absolute servos for this new machine. Looking at delta ASDA A3 servos as the drives have Ethercat support. 
My main concern is not the price of Beckhoff modules. I'm curious to know how the ethercat setup handles the motion control part. In mesa we get the FPGA base step/dir signals and I read the ethercat system uses a target position. So I guess the control loop is closed on the PC with the encoder feedback from the motors. So how fast can you really push an ethercat system without running into following errors and latency errors etc.? I mean like in high speed 3d surfacing ? 

Can anyone offer some advice on which system should I go with or point me to some user experiences?

This machine is in excellent shape I really like to set this up as close to a oem controller.

 

In my experience, Erhercat is no different in performance to Mesa cards. In fact, I found I had to reduce acceleration and max velocity because my motors drove so hard but could not overtake inertia on stopping with Ethercat motors because of the mass of the table and following errors were happening. I just put that down to the normal tuning process as I was asking for speeds too high for machine physics and the motors delivered what I asked for. I would say Ethercat is not for the novice although some novices conquer it. This is because there is the additional complexity added by the Ethercat layer.
The plus side is the Ethercat wiring is a lot simpler.
I would recommend cia402 compatible drives.
With a machine under your belt its is worth considering.

Thanks. I have two machines that run Linuxcnc l. one with 3 parallel ports and running a production job. Other is an old but workhorse of a mill that run the mesa setup. Both are used daily. I'd say I'm good with Linuxcnc but first time using ethercat.

Servos that i choose are beefy. 3kw on x and y and 4.5 on z. Machine is worth saving as it's in near perfect condition. No backlash or spindle runout.

Do you know how the ethercat control loop actually works?