Just to clarify, the bullet type I prefer is a tangent ogive, not esp. the BIB. In the 6mms, in the custom bullet realm, I believe only R.G. Robinett (BIBs) is making a tangent ogive. The semi-custom Berger 108, a recent addition to their line, is also essentially a tangent ogive where it counts most. And when Sierrra gets out a good lot of 107s, nothing is better.
This opinion comes from watching years of shooting. When a barrel "likes" a secant ogive, they do offer, with the high numbers like the 15-cal secant "VLD" design, a real advantage. Older problems of secant bullets were lot to lot variation, and the difficulty of consistency in their manufacture. I'm not sure these "older problems" have all been solved. Rightly or wrongly, I still label VLDs as "fussy."
Brian Litz's addition to the Berger team has given us the hybrids, with some of the properties of a tangent ogive. I haven't shot them except a couple times in my new .338 rifle, so am entitled to no opinion here.
So the 6mms I know of that offer tangent ogives: the BIB 95 and 108 grainers, the Berger 108 (sort of), and the Sierra 107. Too, you may get a barrel that shoots the secants just fine. This begins to rival the .30 bullet selection. I've no quarrel with Greg's recommendation.
BTW Greg, not to hijack the thread too much, but it is an interesting experience shooting a bullet that only looses 900 fps over 1,000 yards, as with the new Berger .338, 300-grain hybrid. I'm not sure I'd want to shoot a 4-target agg with one in a 17-pound rifle, though I guess it's not any worse than shooting two 1K matches in the same day, where you win your relay in both matches.