M1 or Port-Matched LD4B on 408

Jus thinking
5 to 6 seconds gets you 60 mph.
300/350 is more power than most street chassis can handle. From zero to 60, you will only pass thru the power peak once, and in all likelyhood will be roasting the tires at WOT. So on the street, pick one with nice manners for cruising 30mph in Drive at like 1200 or something,lol.
But you didn't build your combo for street, yet you say 50% street, so, it kind needs to be civil.
The LD4B is already port matched.

5 to 10 minutes warm up, at what ambient.
I agree that the street tune in the 850 might need some help. She might need a bit more fuel from the transfers and a little less idle timing, to get the rpm back down. Yeah I'm guessing.