Hi Jack,

I am not a scratch golfer (HCP 6.0) but I will be moving towards a combo set in the coming season.  Here is why.  The benifit of having cavity back long irons is that you have a larger sweet spot and more forgivness than you would with blades. And in many cases you will hit higher shots with CB irons.  Hitting those high long irons will help hold the greens.  The most important thing is that you go get fitted for the combo set so that they can work on your gaps correctly.  They will be able to adjust your lofts or get you slightly different shafts so that there are no large gaps within your bag.

Hope that helped.