I'm guessing it's the neck down that makes them that much weaker. I just went out to the garage to compare. Definitely a noticeable difference in size.

 

1040 has a yield strength of 106,000 psi.
1541H has a yield strength of 164,000 psi.
That is really close to 55%! The 25% increase the websites mentioned is the increase between rolled and cut splines. Sorry you don't believe any of the information I posted, but what I posted is true.

 

30% between cut and rolled
https://www.yukongear.com/axles.aspx

 

I am convinced that it would be worth the upgrade. Probably will just go with revolution axles. Seem to have good things said about them. Plus I can snag brand new ones for about $100

 

Here is the article

http://www.fourwheeler.com/how-to/tr...uck-axle-tech/

SAE Classification Yield Strength (psi) Tensile Strength (psi) Note
1040 106,000 120,000 1
1050 146,000 162,000 2
1541H 164,000 181,000 3
4340 210,000 228,000 4
300M - 270,000 5

Notes
1. Induction-hardened carbon steel, the industry standard for most of the OEM.
2. A higher grade of carbon steel sometimes used by the OEM and the better manufacturers of aftermarket OEM replacements. About 38 percent stronger than most 1040 grades.

3. A high silicon, manganese steel alloy. Approximately 55 percent stronger than 1040.

4. Chrome-moly steel alloy. Excellent strength and resistance to fatigue. Almost 100 percent stronger than 1040

5. Sometimes known as 4340M, it's an aircraft grade of 4340. It has outstanding fatigue resistance. At least 150 percent stronger than 1040, but very expensive and hard to get.

 

so what's being said is, you can swap out the 27 spline guts for the 29 spline stuff? in the same 27 spline axle housing?

 

Housing are the same yes.