First off, I have not had the pleasure of hunting elk with powerbelts. I have only hunted deer.
I do not see why the platinum tip powerbelts would not work just fine. Granted I will admit, if a larger weight powerbelt would shoot as good then I would go with something heavier, but if the 270 is accurate, and you're pushing it with a good powder charge. Place that powerbelt in the right place and if you can distroy some necessary vital organs, then you will have an elk.
The big thing with any animal we hunt is shot placement. If you can not hit where you aim then it will not work. Also then you have to take into consideration the design of the projectile and the powder charge. In this case, the platimum tip powerbelts were made for better penetration then the standard powerbelts. And they are of still enough weight that when they hit vital organs they should do the job.
Good luck to you and all the others who will be elk hunting this year.