Yping - as with anything in this obsessive hobby, gauging performance improvements is relative to the person and their various system components and cables.
I can only state with certainty that each successive model in the gZero line has yielded noticeable improvements and I believe that would be the case on most systems.
So the 20's are like massively upgrading your whole system components...
I have stated a few times on various posts - it is very important that all of your components and cables (power, speaker and IC's) are capable of performing to a very high level in order to get the very best out of any of the gZero line and that especially applies to the gZero20.
But on it's own, I would not say that the improvements would equate to a "massive upgrade" - why?
- the gZero20 can only perform up to the level of your weakest link.
As an example of that, my digital rig sounds very good with the gZero20's, but that sense of "reality", although very good, is not quite as apparent with the DAC I currently own.
However, the gZero20 on the analogue rig, which contains components and cables that achieve a higher resolution, really showcases exactly how good they really are.
Are they really that good?
Yes - they really are!
What they convey are extremely fine details that I found resulted in more reality...
e.g. if a string quartet is recorded in a small concert hall or a church, not only does the gzero20 allow the system to pinpoint each performer with extreme accuracy in a 3D image, but the extremely subtle reverberations surrounding those performers are very noticeable and not only envelopes the artists, but the listener also.
I have not experienced anything quite so realistic, or "holographic", on many of the other 2 channel systems I have listened to. But I have experienced some very nice surround sound recordings on my 5.1 channel system. However, by comparison, I still find they sounded a little contrived.
Are my DIY cables as good as the gZero20? - NO!
They do however, perform better than many other "boutique brands" and because of that I use them on my digital components, since I tend to use that for more "casual listening".
They provide extremely good "bang for the buck" if you are on a budget and depending on the components and wire a person selects, will range in price from approximately $100 (using the Copper Harmony RCA's), to $250 (using the Absolute Harmony RCA's) for a 1 meter pair.
But the analogue rig gets the gZero20 simply because they are capable of conveying those finer details that my phono cartridge and phono stage can provide.
Maybe I should go from my 6s, which I like very much, to the 20's?
That would be a call only you could make.
If money was no object, if there weren't other components you thought required upgrading etc. etc.. then the decision to upgrade to the gZero20 would be simple.
If you are like me - it is not that simple and you have to balance many other choices.
I have given you an account of the details I have observed and since every system responds a little differently to different cables, perhaps your system has already achieved this level of performance.
Since you already have the gZero6, perhaps you should ask yourself
- what is missing from your existing sound?
I have been very fortunate in that I have been able to audition each progressive model and observe the improvements I have mentioned, but those observations may be quite different on another system.
Listening to them first, especially in your system, would be a very wise decision.
Hope that helps