My humble observations:
IMO the GL3 is not much of an overhead caster, it is a tad on the slow side. Others with more experience with it may disagree. The GLX's are nice but big$$$. Isn't GL3 the new name for the IMX?? Maybe not, I am not sure.
Sage DS2'? I doubt it. You can eat a sandwich waiting for that thing to load on the back-cast. DS2 is Graphite II. Juro's Sage seems pretty good, is that Graphite III or IV? Anyways, I will defer to the Sage guys out there on that one, but I do not find even the Sage Euro's to be as fast as the T & T's. Am I wrong here? If so, could someone please educate me on which of the recent Sage's are best at overhead casting? Lefty prefers the Sage Euro 14' 10-weight for surf fishing for stripers, but I believe this model is discontinued???
Loop Adventure/Redington? Bingo! I think you have hit the nail on the head here. Redington RedFly two-handers are the result of the purchase of the designs and I believe some tooling, ( I am guessing the mandrels?) from the Loop fly rods. I have a 12'6" 7/8 weight which adequately casts big heads overhead. Noticeably not as fast or powerful as the big money rods, but it definitely works and at around $ 250 USD, quite the bargain. I am so keen to try out the newer Loops, but they are scarcer than striper teeth here in America. They keep threatening to get a rod in my hands to try out, but it never materializes....
Regarding the 12-weight thing: The DH 1212-3 was not actually intended to be a real 12-weight rod, rather it was designed for overhead casting short 12-weight shooting heads. There was some discussion about how to name the rod for the catalog and a decision was made to name it similarly as the rest of the rods to avoid confusion. Not being a spey guy, I can not tell you if it will actually cast a 12-weight spey line, but I think that Simon G. recommends a 10/11/12 with it.
Why was it designed around 12-weight heads? My idea was this: For a number of reasons, I favor short heads for fishing the surf. One is the high berm which is usually behind you. It is easier to keep a short head out of the dirt. The second is that striped bass will often eat the fly right in the wash, requiring you to retrieve most of the head before you cast again. Short head is a big advantage here, especially if you are repeatedly blind casting. Lastly, fishing as I do, mostly at night, the shorter heads are just plain easier for me to handle. 30' of twelve-weight head is similar in weight to a full-length head of 10-weight fly line, but is much easier to cast and will more easily deliver a bigger fly.
Since this rig is really intended for blind-casting with sinking lines, it did not seem to me that spooking the fish when the line hit the water would really be much of an issue.
Juro had proposed the idea of an 11' 11-weight for this kind of fishing far in advance of my proposing the 1212 to T & T. Personally, after doing a lot of fishing with a lot of different rods, I chose the 1212 configuration because, for one thing, I found that I was very comfortable with the 12' length. It balances nicely for one-handed retrieves, not feeling tip-heavy, and where I fish, the length is not really a problem when landing the fish. I opted for the 12-weight head because it is the largest head which is readily available from a number of different manufacturers, without jumping up to 15, which seems to me, very much like a clothesline in thickness & handling. The 12-weight head really handles big flies nicely. It is barely affected by a 1/0 deceiver, you hardly know it is on there.
If you want to throw a lighter line, the T & T DH1208 the RedFly mentioned above and other similar rods will throw a short, 10-weight head very nicely, but they tend to get bogged down quickly if you want to throw really big flies, or if the wind comes up.
I do not mean to say that the DH1212-3 is the final word for this kind of fishing, but rather I hope that it is the first of a new category of fly rods designed for overhead casting in the surf. I still do believe that it is the best rod I have found for my very specific needs, but then it should be, because Tom Dorsey designed it to be that way.
Try as many as you can get your hands on, and pick the one you like best!
Good Luck.