Not really a difference between the two until you start getting out to about 800+ yards. I have seen 168's keyhole 1000yard targets regularily, they become transonic and unstable at far range. The 175gr. load is my favorite and what I use for F-class. Supersonic past 1000 yards, you will notice a huge difference between these loads from 900-1000 yards. I have hit a target successfully at 1120 yards using a 175gr. BTHP, my longest ever shot. Tried the same thing with the 168's and they were all over the place at that range.
Stick to 175's for stuff beyond 800yards, up to 800 yards both bullets perform superbly and are incredibly accurate.