Thanks for your kind and mindful replies, Chris.
The ability to swap from Factory to Speeduino is an interesting possibility I hadn't considered!
I appreciate your NOx emissions concerns - I'd have no idea how to read an ignition map even if I could find one.
BUT - what I know of the science behind water injection makes me think it would help keep temperatures low enough to prevent and increase in NOx...I take it people around here are electronics-savvy enough to have tried pull-up/-down resistors on MAP sensor signals to ECU/Speeduino?
I suspect it might be in my best interest to see if I can replace the narrowband o2 sensor on my car to a wideband without making the ECU go crazy BEFORE getting deeper into Speeduino.