pulltabfelix --
I'd like to try and provide an answer to your question. You note that you are getting the 10" x 5" Coiltek coil (426g/15.02 oz.), to replace your stock Minelab 11" coil (510g/17.99 oz.), and you noted that this will give you a "nice weight reduction." Indeed, you'll be trimming 3.03 oz. of "coil weight" (a roughly 17% reduction in coil weight) as a result of this switch.
Meanwhile, you asked about a carbon-fiber shaft, and whether it would reduce weight further, by "any noticeable amount." The short answer is yes, it will. The stock Minelab shaft weighs roughly 10.25 oz.; my equivalent two-piece carbon-fiber shaft weights roughly 7.05 oz. -- so, you would be trimming ANOTHER 3.2 oz. of weight from the unit (a roughly 31% reduction in shaft weight), by switching to my standard, two-piece shaft. In other words, you'd trim essentially the same amount of weight (actually just a shade more) by switching from the stock shaft to my carbon-fiber shaft, as you will by switching from the stock 11" coil to the Coiltek 10" x 5".
Additionally, though, what sphillips noted is also absolutely correct -- and probably even more important, in terms of how "comfortably" your Equinox feels, when swinging. The issue with the Equinox, in terms of why it feels uncomfortable to some after swinging it for a few hours, is that it is "nose heavy," or as sphillips put it, the center of gravity is MUCH too far forward. In other words, it is IMBALANCED. So, ADDING some weight, at the butt end of the shaft, works to restore balance -- it makes the machine less "nose heavy" by moving the center of gravity back toward the handle. AND THUS, though it might seem a bit counterintuitive, it actually makes the machine more comfortable to swing.
IF simple weight reduction is solely what you are interested in, then you can certainly achieve that by switching shafts. Again, you shave roughly 3 oz. by switching coils, and you'd shaft another roughly 3 oz. by switching shafts. BUT -- again -- if "discomfort" is the issue for you, then from a shaft builder's perspective, the BEST approach is TWO-FOLD. FIRST, reduce overall weight as much as possible, and then ADD counterweighting, to the butt end of the shaft, to achieve balance -- as BALANCE is, dare I say, even MORE important with respect to a comfortably swinging machine, than simple weight reduction. Both are important, but a lightweight but nose-heavy machine can STILL be a fatiguing, uncomfortable machine for many detectorists (the Equinox being "case in point").
I hope this helps answer your question...
Steve