I've shot some big game with 140 Speer Hot-Cors from a .264 Winchester Magnum, but accuracy varied considerably from lot to lot. I found when using a Juenke Internal Bullet Concentricity Comparator that in some lots there were quite a few poorly-balanced bullets. If I culled those, the well-balanced bullets shot quite well. But without the Comparator it's impossible to tell which bullets are well-balanced, and the faster you push the poorly balanced bullets, the worse they shoot.
My bet, based on some experience, is that if you tried Hornady Interlocks or Sierra GameKing 140's they'd shoot pretty well at 2650, or even faster. In fact I'd bet 140 Nosler Partitions would, because in recent years they've been among the most accurate bullets in several of my 6.5's. But Partitions would probably be a bit pricey for your purposes.
