Stumblejumper:
According to the "Handloaders Digest 1996 15 Edition" on page 82 they show facts on penetration tests using many bullets, and here are a couple facts:
A 130 gr. 7mm Barnes X traveling at 3022 f/s penetrated sauturated telephone books 13.8".
A 175 gr. 7mm Nosler Partition traveling at 3022 f/s penetrated sauturated telephone books 18.9".
This is the fairest comparison I could find on page 82. I don't think 10 grs. more weight concerning the 130 gr. Barnes X bullet is going to out penetrate the 175 gr Nosler Partition.
One needs both Bullet Integrity and SD for a bullet to preform to its full potential. A bullet will not preform to its full potential with only one of the above qualities on heavy large boned game, or longer raking shots.
To start with this is not a fair test because the 130gr bullet could easily be driven at least 300fps and possibly 400fps faster than the 175gr bullet.When the failsafe or barnes x is driven faster the petals bend back more or lose material which decreases cross sectional area.Combine that with the added momentum from the added velocity and there would be a difference in penetration.Checking out the bullet test perfomed in the 1998 edition of handloader magazine shows that the failsafe bullets penetrate most at maximum and minimum velocities and less(up to 5" or more) at medium velocities.The same bullet test also showed that the 165gr,180gr and 200gr speer grand slams(the only bullet used in various weights) all averaged the same penetration although all three have much different sectional densities.So while sectional density is a big factor with conventional bullets it is not always a factor with premium bullets.
My comments on the 140gr partition and 140gr failsafe do not come from theory or from simulation tests but are derived from actual observations of their results on game.I have never seen a 7mm bullet of any weight penetrate more than the 140gr failsafe.Have you actually ever seen the results of the 140gr failsafe on game?