Frank,
Would a tour pro hit each iron farther if he used cavity back, oversize irons instead of small blades?
–Eric, Orlando FL
Eric,
The size or forgiveness of the iron does not dictate the distance the ball will travel if the head weights, lofts, head speeds, and head paths are the same, and the ball is impacted on the sweet spot – which is directly in line with the center of percussion.
The advantage of an oversize iron is its higher MOI (moment of inertia, or resistance to twisting at impact), but that comes into play only on an off-center hit. Obviously there are other differences between irons (typically, oversize cavity-backs have stronger lofts than blades do), but all things being equal a cavity-back iron will hit the ball the same distance as a blade.
Having said this, I have not taken into account some recent designs of cavity back irons, which are now designed to have a spring-like effect which allows the face of the iron club to act like a trampoline and contribute to the efficiency of impact by increasing the COR (coefficient of restitution) which increases the ball speed. This phenomenon of the trampoline effect is difficult – if not impossible — to design into a blade because we define a blade as solid mass. A cavity back club – like a window frame — lends itself to a trampoline type design.
Many of the most elite professionals use a blade, or some design close to it and don’t need the forgiveness of miss-hits as they don’t miss very much and they enjoy the ability to work the ball with a blade and the consistency in the distance they get.
So, should you get irons with spring like effect?
My answer to this is I don’t know why you should because the miss-hits will be a little more erratic as far as distance is concerned, even though the club is more forgiving. So yes to cavity back irons but a “maybe” to those with spring-like effect. If the seven iron doesn’t go far enough take out your six-iron. A spring-like effect is great in a driver – the distance club – and maybe some fairway woods (not “metals” as some announcers have tried to rename them) because there is not another club available to get more distance.
Have fun and I hope that I have answered your question.
Valerie and I are considering creating a podcast to discuss various golf equipment and putting issues. Please let us know if this is something that would be of interest to you by replying below.
Putt well,
Frank
franklygolf 
“If the seven iron doesn’t go far enough take out your six-iron.”
it seems to me that at the lower loft irons, say the four and five irons, if a newer cavity back with spring effect hits farther, then it might be worthwhile to use one as a five iron than a harder to hit four iron blade or regular cavity back: same for four versus three, though i know you have been encouraging players like me to forgo the 3 and 4 irons in favor of hybrids (don’t they have that spring like effect?). and there are differences in the seven versus the six in terms of roll after landing: I’ve always thought distance control was more difficult the lower the loft of the club. this is why I thought the longer hitters had an advantage over shorter hitters: they could hit shorter clubs into the greens with more control of distance, getting closer to the hole or whatever target they were aiming for.
of course, doesn’t matter that much for my level of play, unfortunately (or fortunately),
Frank, like many of your readers, I’ve been playing our wonderful game for a long time – so have been able to enjoy the benefits of club improvements over the past 40+/- years. My mid-sized, forged, cavity back irons are a far cry from my high school era, Sam Snead Blue Ridge irons. I’ve too tried the larger, distance focused irons but went back to the smaller (yet still forgiving) cavity backs. If I need distance, there are the hybrids just one row up in the golf bag. For me, the smaller to mid-sized irons are much better from 100 yards in, and especially with finesse shots around the green. I grew VERY frustrated hitting big 6 irons, only to struggle with chips and pitches. As you say, let the driver spring forth, but let the irons hit their mark!
Thanks, as always for you wisdom and in experience.
Jim