I would say that there are many owner's of both the "Six Series" and the GP100 revolvers, that will favor one or the other of these over the other gun! Also, I think that it is "Incorrect" to state that the GP100 is "Far superior" to the "Six Series"! Superior at what? Certainly, not at everything! The "Six series" are less bulky, easier to handle, has a superior finish(On average)to the GP100, easier to conceal, almost as strong, lighter in weight, has a more "Classic" design", and is prettiier to look at(IMHO)!
On the other hand, the GP100 is built on a larger frame(With more meat under the barrel lug)and has the frontal crane lock, and definately, a more comfortable rubber grip design(Although somewhat "Ugly"!)and is heavier, to assist in better recoil control! Otherwise, there are some other minor upgrades that were "Evolutional" improvements over the "Six Series" revolvers.
I think that it would be more correct to state, that although there were some significant improvements made in the GP100 over the earlier "Six-Series" revolvers, there were some that went towards the "Negative direction(Like the ugly rubber grips, the wobbly ejector rod, the bulkiness, etc.)! :barf:
The bottom line is, that both, the GP100 and the "Six Series" revolvers are great guns! Each one of these guns, have advantages and disadvantages over the other one! But, neither of these revolvers are "Far Superior" to the other one(Overall)! The "Preference" for one over the other, will be mostly a "Subjective" choice(Based upon, variable factors, such as looks, size, bulkiness, recoil control, shootability, whatever?)! Neither of these guns have a history of being a "Bad" gun! Just pick the one that pleases you and you will be getting a good gun, regardless of your choice!