This was the replacement for the IMX rods. The action is pretty similar to the IMX 15 foot 10/11; however, it is a stiffer and faster rod than the IMX simply because the graphite used in it is stiffer than that in the IMX. I personally did not like the GL4's because they tend to be a tip action type of rod because of the increased stiffness over the IMX. They cast OK, but they force you to put a lot of power into the rod to work properly and I don't find that enjoyable to do all day long. NOtice also that G; Loomis no longer makes GL4 2-handers, I suspect because of the incerased stiffness without changing the rod taper from the IMX.
The GL4 2-handers are cannons though because of the increased stiffness over the IMX 2-handers. I was very disappointed with the GL4 2-handers that I cast when they were first produced, and was rather disappointed that G. Loomis quit making one of the nicest 15 ft. 8/9 weight 2-hnaders our of production and replaced it with the (in my opinion) too stiff GL4.
The GLX on the other hand I find to be an excellent and enjoyable rod to cast, which is why I own the 13 ft GLX. The GLX is stiffer graphite than the GL4; however, the rod taper is different and you don't have to work at getting the rod to load as with the GL4.
It will definitely make a powerful rod and will cast the 10/11 GrandSpey or MidSpey with ease. If you are planning on using the Windcutter on it, I would go with the new 11/12/13 because this rod is so stiff.