Solids are not a good idea for Cape buffalo and are not needed for backup shots by a client. The risk of hitting and wounding another is just too great.
When using high speed mono metal bullets for hunting Cape buffalo you will be seriously limiting your possibilities of taking a shot when using these. The possibility of the bullet shooting straight through the buffalo is real and you will be responsible for any other buffalo killed or wounded. This will result in a dangerous situation if you need to deal with 2 wounded buff from the same herd.
Most buffalo hunting will be from herds and rarely will the opportunity arise where you will be lucky enough to be hunting single or small groups of dagha bulls. If you are absolutely sure you will be hunting single or small groups of dagha bulls, then it is not so significant.
The ideal buffalo bullet has always been a heavy for caliber controlled expansion bullet. For the 375 H&H that is 300-380gr bullets. The bullet should hold together and not exit but rather be found on the opposite side just under the skin.
You normally pick up fresh buffalo tracks early in the morning, close to a watering point, as buffalo prefer to drink twice during the day, start tracking and hopefully catch up to the herd as the day warms up and they find shade to lie up during the hot part of the day and ruminate. Not all stalks will be successful and many miles could be covered over a number of days before finally you get into position and spot a good bull. If you now find the once in a lifetime buffalo is standing in front of another it would be impossible to take the shot if the bullet you are using is possibly going to exit.
If you are an ethical hunter, you will now have to sit and wait and hope your bull decides to somehow move and clear any buffalo behind it. It is now the hot part of the day, the wind is not constant and keeps swirling, suddenly you get a whiff of wind on the nape of your neck, the herd gets your sent and the whole lot thunder off. Your trophy bull disappears with the herd. You may try another stalk but by now the wind is all over the place. The call is made and you now have to walk all the way back to the cruiser that you left 5 hours ago.
Had you been using a North Fork, Swift A frame, Trophy bonded bear claw or the excellent Rhino bullet in a weight from 300-380 gr's at a mv of 2200-2400 fps, you could have taken that shot and you would have had your once in a lifetime buffalo.
If you can control your shooting and only take shots with no buffalo behind and be prepared to pass up your once in a lifetime buffalo because another is standing behind it, then use a 270 gr Barnes TSX loaded to the highest velocity you can get from your chosen rifle if you like, if not, then rather use the sensible well proven, option of one of the premium grade bullets mentioned and give yourself all the opportunities of getting your once in a lifetime buffalo.
The realities are that the "perfect shot" is not always available when hunting Cape Buffalo, so why limit yourself further by using a bullet that restricts your ability to take a shot when it presents itself?