How often do you plan to do this benchmarking? If a table has tons and tons of rows, the count(*) can take quite a while. If the benchmarks are taken at about the same time that runstats are executed, then you can just query the syscat.tables view like this: select tabschema,tabname,card from syscat.tables. It will not be 100% accurate, just when the last runstats ran. But this maybe all you need.
HTH
Andy