DeanWs

If it feels like it is shutting down, I would start by setting set up ECU logging, record battery voltage, a few other common variables as well as trigger stuff at 100Hz.  That should at least show if there is any shutdown going on due to lose power connection or if it is just a misfire.  

As a general rule the peak current will be around 60% of the total draw in current found in ohms law, this is because we are not actually dealing with resistance but magnetec inductance and the solenoid coil will start making maximum magnetism well before coil saturation however the only way to really tell is to watch it with an oscilloscope.
So in your case at 14v the current drawn in ohms law would be 5A like you said so 60% of that will be 3A and the hold current will be 25% of that figure 0.75A and the requirement will rise slightly as fuel pressure rises.
So I would try 3A and 0.75A

Nissan twin cam coil packs ground the high current side through the coil pack body (transformer core) to the head.
They have a high current 12V supply, ECU trigger reference and a low current ground through the plug.
Those injectors should be fine, they should be around 4 ohms?