Hello,
Sorry to hear about your back.
I have experience with the cabs you're talking about. Here goes:
The neos are the answer for your back. They are the most light weight. I've done a load of shows with neo 10s and my back thanks me. In fact, I've toured running through a first gen GK MB210, which is a combo amp with 2x10 neos. It weighs no more than a case of wine. Really. This model was replaced by the MB210 II which almost the same thing with ceramic drivers. It weighs a little more but still very light for a combo.
The CX210 is the answer for your tone. I use two of these to get a 4ohm load for my amp (GK) but the rig remains modular which means I can fit it into my car easily with plenty of room for the other stuff. I can pick up a CX210 with one hand. I can pick up one in each hand and raise them above my shoulder. But I do work out. They are definitely heavier than a 210 neo cab but again, easy to lift. You can get the weight specs from GK's website.
Tone: The CX 210 definitely has more low end response. High mids are more present in the neo cabs, but the CX can pretty much cover it all. I don't use the tweeter, but I can see how some would. For large venues, neos or ceramics would work fine because you're using FOH to move the air. The neos are edgier. The CX is darker. I sometimes hook up a CX210 to the MB210 and run a neo/cx mix. Sounds great, I think I accidently cut down a neighbor's tree with that sound.
Tuning: Yes, the CX210 can handle alternate bass tunings. Know why? Because when you're playing metal tuned to A or G# no one can hear your low fundamental anyway. There aren't any cabs designed to reproduce that. It's the harmonics you're after. The ones that tell the ear that that note exists. The CX210 can do that. Please remember, just because you're playing low notes doesn't mean you need low frequencies.
To sum it up: The CX210 can do what you are asking for. I use them, and recommend them. GK no longer makes a neo 210, so the CX is the way to go if you need modular. If you want 12" drivers, everything I just wrote applies, but everything is heavier. I also recommend core strength training. If you're 25 with back problems, you need to train your body to avoid injury. Good luck!!