I've not tried an 850DP yet inplace of the 750, but it will be down on fuel mileage and throttle response some...not a big deal as throttle response doesn't dictate actual power made. It just sounds cool in Park!!
I'm not sure about a 4150 series 850 (DP). The VS 870 Avenger gets over 17 on a street 422 w/3.23s in a heavy E body and there is no throttle response issues. Just lots of traction issues.
I'd say any dyno info from that 408 build is almost useless for the engines most here are building. Not to mention that once that engine's in a car racing the differences you make of note won't mean **** and it will be back to the drawing board for baseline tuning.