Holley question

What is so different about Holley's 4150 "HP" series as opposed to the other Holleys? Pros? Cons? I was just paging through an old Summit catalog, and noticed they cost nearly twice as much.......I can't seem to find a definitive answer on the internet either.......:confused

The HP come with notched floats, jet extensions, adjustable air bleeds, stainless throttle plates and 4 corner idle. Not sure if a non-HP has some of that or not.