[JP Noonan]

I've been told it is the difference in duration and overlap that throws FI off, if the duration is about the same and only the lift is a little higher FI should work.

Duration and over-lap cause lower vacuum and can cause intake gasses to be blown back into the intake. Carbs handle this fine, the turbulence helps keep the fuel in suspention. FI can't cope because intake air volume is inferred by engine vacuum.

How much is too much, I dunno. Ask the cam manufacture.

BTW did you put bigger valves in the heads?