I'm down in Florida (North Central, around Gainesville area.
A LOT of people think that going with a 'mild' cam is good for FI, and generally, that's true. Fact is, any cam will make power with FI - the engine system is just that, a system. You want to match ALL the components together! Many 'builders' go with a mild cam, because it's easier to tune, that's all.
In your case, you don't have a 'mild' cam, you've got a downright anemic cam!
General rule of thumb is that the larger the displacement, the more mild a given set of cam specs will act. A 207/220 cam on a 118.5 LSA would be mild in a 5.3L, nevermind a 6.7L!
With a 4" stroke, you have nothing to worry about regarding low end torque, LOL. Decide where you want your powerband to be, and work from there.
I'm not familiar with PLX Devices, although the website shows they have a WBO2 0-5v output, so that's what you want run to the MPVI Pro. Are you saying that you are getting intermittent readings? I'll see if I can track down a diagram and find out exactly which wire you need.
I use a Zeitronix ZT-2 (http://www.zeitronix.com) that I've had now.. 7-8 years? She's been flawless over many vehicles
What gears and tires are you running? Still running the S6-650, right? Average highway cruising speed?