I am not sure you can get reliable max dmips values from a datasheet. The microblaze IP core is highly configurable which will greatly impact the max dmips for that implementation of the processor. Typically a microblaze implementation with a higher dmips will use more resources. Of course a microblaze that is configured with a hard floating point unit will use more resources without performing any higher dmips.
Ted Booth - Tech. Lead FPGA Design Engineer www.designlinxhs.com