I know I'm late to the discussion, but one fact to consider is the RPM range. While a specific carb may make more power on the dyno, you need to be careful and look at the RPM it made it at. If the engine makes 75 more HP but it was 1000 RPM higher, you may not be able to use it.
Also, when looking at carbs, the intake style plays a big part. A stock 454 with a dual plane may like a 850 best, but throw a single plane on the same engine, and it will probably perform better with a 750.
Once you start getting into large cams and such, your airflow requirements can go through the roof, but you also have to turn the rpm's too. Jets have the handicap of the hard stop rev limiting impellor unlike cars that have nothing to really limit the RPM.
IMHO - Sleeper you need a bigger carb than 1250 :-)
My 528 is running 1660 CFM, and it is under carbed. Usually if you have to jump more than 5-6 jet sizes up from stock, you can gain more by switching carbs.
