I've always run holley 4150 double pumpers... nothin' fancy standard main body. had a 750 with the choke tower milled off now running a 850 race with big annular boosters... will mill the choke tower off that one shortly. I've had issues with each but with some persistence in going after the tuning both ran perfectly. As for your idle transition stumble it sounds very much like a vac leak (been there done that) could also be idle circuit way too lean or not enough pump shot...

Hope some of this helps... thing is all these proform quick fuel BG etc etc are all basically just Holley's in fancy clothes

-Chris