Comparing performance in between differnt plattforms is a difficult task, this is just a very basic aproach:
dd if=/dev/zero of=test bs=1024 count= => creates a file of 10 MByte
time bzip2 test => compresses test to 49 Bytes
This test only requires integer arithmetics, if floating point operations would have to be simulated, the results for the slug would be poorer. To summarize it: The performance is about 5..10% of a performant PC-system, but for many applications this is more than enougth.