Leaf Blowers

looking at buying a backpack blower model 150bt..but i am confused your specs say it has 251mph with 710 cfm.how can this be if model 350bt which is replacing 150bt has only 180mph and 494 cfm.they are both 50cc engines..i am looking at other brands and most are in the range of the 350bt specs.fyi the specs i am referring to on the 150bt are on the box at lowes.can you explain? also i called one of your dealers and they could not give me an answer either.how can i buy a product when noone can explain it to me???