>>needs to open up at low velocity
Why? .375 is not enough for you?
Richard plans on making one (or so the rumor goes).
My 375 RUM shoots the 260gr AB really well (not really a high BC, long range bullet). It also likes the 300gr Sierra. Come to think of it, Kirby's creation seems to like anything I load up in that gun.
Haven't shot any critters with the 375, but judging from the rocks it busts up I'd say it should do fine on elk.
I think there are plenty of us waiting for something better than the 260gr AB.