A stock 44 is probably 100% stronger than a stock CJ 30. That is comparing the strength of the axles as complete assemblies. That being said, a modified 30 can approach the strength of a 44. I am currently running a Dana 30 in the front of my CJ. Mine has Warn shafts, 297 joints, a Detroit, and 5.38 gears. A 44 is stronger than my axle only in the strength of the R&P. My Detroit is not going to break any easier than a 44 Detroit, My axle shafts are stronger than stock 44 axle shafts, and I am running the same u-joints as a 44. As for the comparative strength ot the R&P sets I have heard the same 15% number you have, I have been told that by highly respected gear vendors and axle builders. Personally I feel that that is a little low. I would guess that the 44 R&P is 25-30% stronger than the 30. However the 15% number I have heard comes from guys who know more about this than I do.
I have slowly changed my opinion on the value of swapping in a 44. For someone who has a stock 30 it makes some sense because the cost is similar to building up the 30 and you do get a stronger R&P. For someone like me or you who has a 30 which is built to be nearly as strong as a 30 can get swapping in a 44 does not make a whole lot of sense. The 44 would not be a significant upgrade for me considering the costs and benefits. Unfortunatly I have come to this conclusion a little too late, I have a 44 nearly completed and sitting in my garage.
For you I would say get the Detroit and run your 30 while you think about whether you need a stronger axle. If you add the Detroit you will have essentially the same axle as me, and I have beat the crap out of mine with no breakage (so far). Your weak link is the stock carrier and lock-rite combo, eliminate that and you will have a very stout axle. If you then feel that you need more, you will be in the same boat as me. My opinion is that the 44 I have built is not going to be enough, I'm probably going to have to try to sell it and build a 60.
BTW the most common breakage I have seen with Warn axled 30s is the u-joints. They give it up, and sometimes take the Warn shafts out as well. I have seen a few torn up R&P sets, but it is mostly joints. CTM joints would solve the joint problem and are applicable to both 44s and upgraded 30s.
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