PPC speed differences

Has anyone done any research into relative speeds of PPCs cpus, specifically Mips compared to Arm? The reason i ask is because i'm working on something for ARM cpus which is quite cpu-hungry and am still contemplating the feasability of a Mips version. I'd hate to spend a lot of time on specific optimisations & tweaks for a Mips build, only to find out it can't run at a decent speed.
Any thoughts are appreciated, especially if someone has done any kind of benchmark testing.
Any thoughts are appreciated, especially if someone has done any kind of benchmark testing.