It just sounds like you don't have need of the added benefits and features of the 1D X. I'll state that the loud shutter is a really important point, and probably the most significant and helpful thing I've heard from anyone so far who does wildlife and bird photography. I worry about the shutter sound on my 7D, and I know even it has scared things off at times. Knowing the 5D III has such a quiet shutter is a really critical bit of knowledge, and may be the tipping point for many who want a great wildlife camera (even if it costs them a bit on the frame rate front.)
That said, there are many reasons to get the 1D X despite the 5D III's quieter shutter. For one, at higher ISO settings (WELL above ISO 1000, like 16000, 20000, 25600) the 1D X kicks the crap out of every other camera on the market. It may not be that important for wildlife, but in the case of bird photography, especially birds in flight on overcast days (when light, while dim, tends to be very nicely diffused), having very high ISO settings that are usable can mean getting or not getting the shot, and being able to print it when you get it. The 5D III has at least one stop less latitude in that area than the 1D X, maybe a bit more when using RAW...and that could be far more important than a quiet shutter.
Having a higher frame rate is also very useful, often in the same circumstances that very high ISO is useful. It does not guarantee you any more than the 5D III's 6fps, but having double the frame rate doubles your chances of nailing a better moment. If I had to choose between the 5D III 6fps and 7D 8fps, I'd pick the 5D III these days. I may even pick the 5D III against a camera with 10fps, but 12fps is DOUBLE, and for high speed action like birds in flight, it can be one of the more critical factors in getting the shot. With a proper blind, the shutter speed shouldn't be as scary as if you were simply in camo clothing (at least in my experience, the 7D shutter sound can be "scary" to birds if I'm not in a blind, but largely inconsequential when I am in a blind.)
Regarding the battery grip.... the 1DX only accepts one battery in the grip and the life of the battery (at least the one I got from CPS) only gave me two days of shooting before I had to recharge at 50%. I unfortunately didn't check the shutter count...though I was chimping a lot and that does have some impact on battery life. The 5DIII takes two batteries in the grip and I can usually shoot for 2 weeks before needing to recharge around 50%. Not a deal breaker by any means though just means you need to carry that extra battery in your bag and take the 5lb charging station with you on extended trips.
I'm curious what you mean by "recharge around 50%". Do you mean you are only draining your battery TO 50% before you recharge? If so, then I think you are greatly skewing the longevity of the 1D X battery. Personally, I use my batteries until they are nearly drained. I'll keep going and going until I start sensing increased shutter lag, which happens when the voltage drops below a certain threshold (which in the case of Canon batteries tends to be only shortly before the battery is completely drained.)
If you are saying you get 2 days of shooting on 50% charge, that would mean you should get around four days of shooting on a single full charge. The 1D X is definitely a higher powered body, particularly when operating at double the frame rate, and more so if you are backing up every shot to a secondary card. On top of that, the 1D X supplies more power to the lens for AF drive.
I'd also offer that you seem to be getting some very surprising longevity out of your 5D III battery life. Either you are using the 5D III in a very different way than the 1D X, or you have extra high capacity batteries or some thing like that. The 7D uses the same batteries as the 5D III, LP-E6. I have two of those in my battery grip, and under heavy use (filling up four to six 16GB memory cards a day) I can burn through the entire charge of both in two days or so. Under lighter shooting, they can go for about a week, but I'd be hard pressed to get two full weeks out of only half the charge...that would be over three weeks out of a full charge.
If you really do charge at 50%, I think you are probably wasting a LOT of the 1D X batteries potential. You should be getting the average power out of that battery until it is nearly empty. I am not sure you can get a full two weeks out of a single batteries charge, but you should certainly get more than two days.