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If you are talking about the 6D, it has built-in Wi-Fi and Canon has free tethering software for both computers and mobile devices. http://www.usa.canon.com/cusa/consumer/standard_display/cameraconnect_app_features http://www.usa.canon.com/cusa/consumer/standard_display/EOS_app http://www.usa.canon.com/cusa/consumer/standard_display/eos_utility These are ...
I have a couple of Eye-Fi's....Pumped 10,000+ pics through the main one (jpg/RAW/video), with nary a burp, from a Fuji HS-10. Never done it to an iPad though...just directly to the main PC or laptop.
What you are looking for is called tethered shooting. With a laptop or a USB OTG enabled Android device, you need nothing more than a USB cable and some (free) software. E.g. Canon's EOS utility, or Lightroom, on the computer. With the iPad, you are out of luck in this regard, AFAIK, apart from your mentioned EyeFi solution.
In windows task manager, you can lower the priority class of the Lightroom process. That will help other processes to get some more CPU time, and quite frankly i think Adobe should have implemented those long running tasks with idle priority anyway, so working interactively could continue as normal. You also can fiddle with CPU affinity of the Lightroom ...
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