new asm disks

My asm disk group is composed of 72 gig 15k rpm disks. I have new 320 gig 15k rpm disks that I want to add to the database, eventually replacing the existing disk. While the disks spec to be the same speed, they were made about 2 years apart, so I'm guessing there is still a difference in performance.  

Question 1, is it still ok to add the new disk to the existing diskgroup and rebalance the old disk out?  

Question 2 would it be better to create a new disk group and then figure out a way to move the tablespaces to the new diskgroup?  

Thanks

Randy  

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