Holley 2 stage power valves

So, on a 650 Holley spreadbore carb list 7004-1, is there a benefit to running the 2 stage powervalves over the standard single stage ones? They are discontinued for one. Holley claims they aid in economy. The one in the carb is fine, I was just wondering. Holley replacement PV is a 6.5. The 2 stage is 10.5/6.5 Would it make a difference to change it out for a standard 6.5?