Let me add some comma's.

"In any case, there is pretty much no time ,out on the street, I can aggressively put the pedal to the floor without the tires starting to break loose on the pavement, so plenty of fun for street driving. And as I said, it gets 17+ mpg."

Basically in the first four gears on street tires if the pedal is on the floor the rear tires have no traction. Either on the track or on the street. I've never met a person with a carbed 450+ cubic engine engine cranking out 500+HP getting over 12mpg. Especially with steep gearing. Being significantly lean is why it did not make the power before, that and being nearly 1,500rpm under it's powerband for half the track.

I've done plenty of idle, cruising and WOT blasts with the cut outs open and closed. No video, but plenty of datalogging. Not hurting for data in that respect. Believe me I was expecting a change, but it did not happen. I think most people get an AFR change from reversion up the collector to the sensor, my cutouts are almost three feet past the sensor, so no reversion issues messing with the sensor reading. That and the EFI compensates for efficiency changes far better than a carb.

Fortunately the guy doesn't need the website to stay busy, he's got enough backlog of work from reputation.
Rebuilding an OHC Pontiac 250 with EFI and a Turbo