The only experience I have with a street driven 2x4 setup was on a '68 Chevy Impala with a Tunnel Ram and a pair of 1850 600's. The carbs had the equalization tubes removed and the holes plugged. Everything else has been dual race carbs, 660's, 850 DP's, 1050's, 1150's, split Dom's.
My 660's are stock with no modifications and had no bog or flat-spot, it was like turning on a light switch, BAMMM!!!!
I agree with Brian's first couple of sentences, as far as the going fast part, if we're talking street driving, with occasional jaunt's down the 1/4 and decent milage when your off the throttle, I've got no problem with that. If you don't care about mileage or tickets and know how to make radials stick, the performance of a proper multi carb package can't be beat. The thing is, I don't condone street racing or testing on the street, but if you drive your car to the track, kick some GM tail, then drive home, that's great.
My race 289 with '69 351w heads ran 11.0s with the 660's. With ported Canfields, a Funnel Web and a Pro Systems carb it's run 11.90's. Now the first was a Jerico and the second, an $1800 PA C4, but I don't think a race C4 is worth 9/10s.