Joe,
Although I have found my T&T 1611 can cast the whole belly of the 10/11 GS, it is not happy doing so unless I limit myself to casts os less than 80 ft. I use the 9/10 GS on my 1611 and love the way it feels all the way from 50' to over 100'.
I'd love to use my 10/11 GS in winter because of its use of 11 wt tips, which sink a little faster than the 10 wt tips I use on the 9/10 GS. However, the 1500 gr wt of the 10/11 slows down and feels heavy on my 1611, so I don't use it anymore. The 10/11 XLT feels very nice on my 1611 though and it weighs about 1240 gr, which is nearly the same as the 1300 gr of the 9/10 GS.
You perfectly described why I have been saying I want to see a rod manufacturer put a fast-recovering, stiff, powerful, progressive loading 17' 12 wt on the market. I would be able to cast the 10/11 GS's 1500 gr as well as my 1611 casts the 9/10 GS. Rod makers, there are others of us out here who are desireous of a fast, stiff, powerful 17' or 176" 12 wt so we can use the 10/11 GS and cast its 1500 grs, to the middle of the river if we wish. Perhaps, one of them will produce such a rod for we big line, long rod affectionatos withing the next year or so, (I can hope and dream can't I?)..