Well I don't recommend overclocking a "brand" new card immediately. But here are the core/memory speed for a 9800XT
Core: 412MHz
Memory: 365MHz
The default speeds for a 9800Pro is core 380MHz and memory 340MHz.
I'm not sure what's the safest way to overclock ATi's cards but you could use RivaTuner and remember overclock in small increments. Up the speed by 5-10MHz, preferrably 5MHz.