I have never used gamekings but you can't go wrong with the bear claws or partitions and the gamekings have a great rep. as well.

The TBBC's are my favorite bullet for punching through thick hide or heavy bone. I've never used a sierra bullet in the field.
If I'm in the thick brush where close up and personal is expected. There will be a TBBC ready.
The trajectory is a tad bit different than the chosen bullet, for either rifle. At MPBR the TBBC's drop an additional 2" and are about 3/4" higher at the peak of the trajectory.

It's not that the Sierra is a flat shooting bullet, but rather that the .270 in general is a fairly flat shooting cartridge when loaded to it's old-time "original" loading velocity of over 3100 ft/sec. Even the modern full power factory load at 3060 ft/sec is planty flat.

What bullet? The answer depends on what you are planning to hunt with it. Pronghorn, Deer, Elk, Moose????? Most game that you will take with a .270 rarely require a tough bonded expensive bullet like the Trophy Bonded Bear Claw or the even a Nosler Partition for that matter. You really don't need them even on elk. Those tough bonded expensive bullets are best used on very tough large animals like Grizzlies, Polars, or Buffulo. Basically game where you will be using a larger caliber rifle.

I've been using the Hornady 140gr SST and the Nosler 140gr combined techonology blastic silver tips. I really like the Nosler CT but the partitions will probally be the next load I work up for that gun.

140gr partitions are the best. I use the 150gr in my 270wsm. They are the best you can buy! IMHO.