My "little" 350 with a 6-71 seems to be pretty happy cruising the streets and highways for the last 20k miles or so. i drive it rain or shine and have even driven it in the Minn snowy winter. 2x 750 dp work great. I have worked with them for a long time and now get 16 mpg aver and I have hit 17 several times for extended drives. I run on 87 to boot.
It's pretty hard not to make 500+ hp with a 6-71 on a sbc. Compression ratio is the biggest hurdle.
Now just to get a couple of posters corrected......there is quite high vacuum under a 6-71 or any positive displacement blower. there is also higher than normal vacuum directly under the carbs all the time. maybe an inch or more.
Boost will come instantly if you jump the throttle however if you are gentle there will just be a reduction of vacuum. Much of the cruise power comes from the very good fuel atomization and great fuel distribution the blower provides by thouroghly thrashing the fuel/air mix. Granted there is some heating of the mixture but this is not all bad as along with this there is little or no puddling of fuel in the manifold that you get with hot cam and low revs NA. Often the idle improves dramatically. My motor used to idle at 1100-1200 in neutral and was barely drivable in heavy traffic. Now it idles at 750 in gear just like any other car on the road. I can sit in traffic as long as necessary with the AC on. There is no Detroit roll ever.....the mark of poor tuning...save it for the Pro Mods...ugh.