For any given velocity, the higher the BC, the higher the retained velocity - regardless of diameter or weight.
: If both 140's and 120's have the same BC- the 120's will always be faster, shoot flatter and in the case of the TX, will probably penetrate more deeply than a normally designed 140gr. bullet.

I did a similar change with the .260 CLC I designed. For long range shooting, the 120 XLC's at 3,308fps were condiserably flatter shooting than any of the hunting 140's when driven at top speeds of 2,850fps.