Thanks for posting your thoughts and results
I seem to remember IK Multimedia saying their apps are optimised for the specific device it is installed on. This means if you had a newer device you would probably get more polyphony and better latency.

Personally I would still use an independent module if I could although this could be because I have not tried sampler or synth apps on a gig, and if I did, would not be sure I would want to have that same device multitasking my charts.

I was also thinking about (non) balanced cables and hum. I would probably use a short cable from my iOS device to my DI if my amp was not near me to eliminate any interference that might occur, although I am not sure how common it is with guitarists using iRig (etc.) in gigging. I have not had any problems with Ampkit Link and guitar cabling to an amp (not that I have tested this extensively.)