I don't have experience with the .35s, but I can tell you from the good and bad reports on other forums, and experience with other calibers of the FTX, that it seems to be highly dependent upon the bullet in question.
The .308 MX bullet, for example, is tougher than the .30-30 version (as I see Roadkill hit upon).
The .35 Remington version is, of course, different that either of the previous.
And the .44 caliber FTXs are intended for completely different applications, as well.
One explodes, without fail, at rifle velocities (it's a handgun bullet); while the other fragments frequently, but not always (the actual "rifle" bullet).
Even the 325 gr .458" (.45-70) version, which is intended for nearly the same applications as the 265 gr .430" (.444 Marlin) bullet, performs differently. They fragment in their own ways, shed jackets differently, and seem to expand at different rates.
After the testing that I've done with the bullets at or below their intended impact velocities, I don't trust any of them. They sure to put a hurtin' on what ever they hit; but not in a predictable, repeatable manor, unless impact velocity is so low that the bullet barely expands (if at all).
There's no way you'd find me stuffing the .35 Remington version into .35 Whelen while expecting anything other than complete failure.