CFM = Cubic feet per minute , of air that is, The more you have the better your cleaning, However Lift and CFM have a anti relationship as one goes up the other goes down, The trick is finding the sweet spot.
To give you an idea of to much lift, If you piped in a guage into your hose and then put a marble on a table, put the hose over the marble and seal it tight. Switch the machine on and the lift gauge will show maximum lift, but the marble will not move, lift the pipe slowly and the marble will race down the pipe as air rushes in and carry's it away. a vacuum cleaner is just a pump that carry's dirt by means of negative pressure in air.