Vette447,
In answer to your questions.
The S&B 175gr is not "officially" retailed in the USA. It just so happens that the VP of sales for Magtech (owner of S&B) is a 7x57 guy so for his own purposes, he has imported the coveted 175gr Partitions. They are available directly from magtech I believe, or they can direct you to a retailer that can special order them. Not quite sure of the authorized process but bottom line is they have/had them in their US warehouse. The VP is also a regular reader on this forum and that is how I learned of their availability 18 months ago.
Yes, drop is a factor with a 175gr bullet at those speeds. With a 200 yard zero, at 50 yards you're 1.37" high. At 110 yards you've plateau'd at 2.72" high. At 200 yards you are back to zero. At 235 yards you're roughly 3" low. So for Maximum point blank range, I'd say its a gun suitable for out to 235 yards which happens to be about the maximum ethical range for shooting off sticks in my opinion. My longest kill was a 221 yard impala shot off sticks in Zimbabwe and that's about as good as I could do.
Now if you ignore the maximum point blank range because you have a ballistic calculating rangefinder (Highly recommend the Leica HD-B 10x42 range finding binos) then it will give you firing solutions. I'm a believer that the partition bullet and the caliber itself were designed to kill game between 1900fps and 2400fps. Therefore, at 340 yards the bullet is traveling 1905fps with a significant 17.5" of drop. That's I'd say about the maximum drop a reasonable shooter can hold over on a medium sized animal like a kudu, zebra or impala. Everybody knows what a foot and a half looks like and it means if you shoot just above their shoulders, you will hit them in the kill zone.
Many people will suggest you go with a really powerful rifle to avoid these limitations so lets look at the most commonly recommend rifle for Africa, the 300 Win Mag. 3000fps pushing a nosler partition 180gr bullet with a BC of .474. (this contrasts to 2430fps with a partition 175gr with a BC of .519 in 7x57). We know what you lost by going to the .300 Win Mag. You have heavy recoil. You have a heavy gun. And what did you gain over the puny 7x57 in the important areas of Maximum Point Blank Range of 3" and reasonable kill speed of 1900fps?
The 300 Winmag is at 3" of drop at 265 yards with a 200 yard zero. All that extra bucking recoil and heavy lugging gun bought you 30 yards of Maximum Point Blank Range of 3".
The 300 Winmag does afford you a 1900fps minimum effective operating speed for proper bullet expansion at a very distant 600 yards, a 260 yard further distance than the 7x57. BUT, BUT the .300 Win has an astounding 66.66" of DROP at that 600 yard mark or put simpler, the bullet is dropping 5 and a half FEET at 600 yards. Unless you're playing mil spec with drop tables and fancy adjustments to windage and elevation, you're probably not able to "hold over" 5.5 feet to get your kill.
I also question the efficacy of a Partition bullet hitting at OVER 2400FPS because jacket separation can be a real problem. The 300 Win Mag doesn't hit that performance sweet spot in our example until the 300 yard mark. Simply put, the bullet is really traveling too fast to operate optimally until the bullet is beyond most people's comfortable shooting distance. I even had jacket separations occasionally at close shots with a 7x57 so I can't imagine the problems that would happen at hyper velocities out of a 300Winmag.
So at what yardage does the 300 Win Mag provide you with that 18" maximum responsible hold over in the scenario outlined? Answer: at 390 yards. A 50 yard further shot can be made with a 300 winmag using the 18" hold over maximum as the basis for a reasonable approach.
It seems that the 300Win Mag provides much more pain to shoot and gun weight to lug around to provide an extra 30 yards MPBR and an extra 50 yards of theoretical "aim for top of back" shooting. I'd say the picture gets a bit more grim when you consider there are probably fewer than one shooter in 1000 that can shoot an animal at 390 yards off sticks responsibly which in turn completely neuters the "bring a faster gun" argument for me.
In conclusion, not trying to bash the 300 Win Mag but trying to exalt the 7x57 because it provides such an amazing group of capabilities with no pain to the shoulder in a lightweight stalking rifle. Consider the fact that you may not have come halfway around the world to hunt game at great distances and you're left with the reality that for spot and stalk (why most come to Africa) the 7x57 is absolutely ideal for most applications.