For either 6.5 or 270, it's not that hard to find bullets long enough and pointy enough with super high BC's to require quick twist barrels. The trend in long range target shooting in fact appears to be 270's with 8 twist barrels.
Something to keep in mind, it is easy for any manufacturer to make higher BC bullets. But they know that longer bullets become much fussier regarding seating depths and accuracy. In target bullets the Sierra Matchking is an easy example, people look down on them because Bergers/Lapuas/etc have higher BC's. But the Matchkings are much less fussy with seating depths and finding accurate loads.
For hunting purposes, it's not worth worrying about the difference.
