We've had good success with Abowyer brown bears. They are definately heavier than Zwickey's. But as stated above, heavier is usually better with tough, big animals like a bull elk.
I shoot a 58# R/D with a 640 grain arrow (300 total up front) and passed through my bull last year. The two previous bulls it lodged in off side bone. All three died within 100 yards.
Regardless of your choice, at 10 grains per pound thats 630 grains. I'd start around there and adjust to tune. My two cents.