Can a Quality Full Range Speaker be the Limiting Component in a system?

There are a few slippery, impossible to absolutely define, phrases or assumptions in your inquiry, such as;
"... quality full range speaker"
"... limiting component" 
"... bottleneck" 
"... speaker's performance has been fully optimized" 

Now, if you get those parameters sorted out you can answer your question.  :) 

david_ten, there is no way to assess components of a different genre in consideration of their absolute value to each other. All such comparisons are relative. You simply have to assess the performance of a component in a system. 

What is it you are trying to discover? There is no absolute correlation between the performance of a speaker to another, nor to components. It is a complicated network and to date we cannot isolate the interactions. 

folkfreak, politely I disagree with your assessment. Your system and experience could be elevated tremendously with different speakers, or ones up the line. This is no dismissal of your fine transducers, but merely pointing out that there are always many, many rungs on the performance ladder to climb if so desired, and upgrading speakers can in a moment, even when dropped into a current rig, scale many of those rungs. Personally, if I had the means I would not opt for a lesser speaker, as too much in terms of performance/experience is left on the table. All speakers can be improved with components and cables, but you are still bound by the hard limits of the speaker's performance. The odds are very good that with a speaker upgrade even if the system is not optimized for the new speakers the sound would be perceived as dramatically/holistically superior.  

Your methodology is not wrong, unless you have the means, yet are opting for a "budget" solution when it comes to speakers. And yes, I'm aware you have Magico speakers.  Imo, regardless of the system budget, 10% into transducers is severely restricting performance. Note that I am discussing this relative to your situation, not relative to the average audiophile's system/sound.   :) 

I would do bigger, even much bigger speakers in your room. You have the potential, if you wish, to put a rig together that would humble the current one, but it would have to be with greater transducers. Could be done easily with the means and desire. I would have a 6' speaker in there and it would sound glorious.  Everyone has differing priorities; I'm just saying that if I owned that room I sure wouldn't stop at a smallish speaker.  Imo, too much handed away, regardless of the pedigree of components.  :)

Al, the problem with assessment of speakers by headphones is that there exists as much variance of performance between headphones as speakers. You would need a set of several headphones to peg the performance of the headphones if they were to be used as a measure of the speaker performance!  :)