you could be lucky, increase th clocks only a little bit and then try to run superpi and 3dmark benchmarks to see if it runs stable. but be careful - you can fry your gpu by overclocking it.
i have a x1660mobility 128mb core 440 / mem 375 when i set the mem to 450 and set core to find max core it goes above 600 then i stopped i was afraid it wil frie.