Well no one can just tell you "152.33452123 mhz, anything lower will work for you buddy!". It varies from system to system. You should stress test your computer with Prime95 running for 24 hours, and running 3dmark2001. Another really great test for FSB stability I have found to be usefull is to open a large video file, preferably divx4, and try to skip around the file going really far into it, way back, then forward, just do it a lot and make the computer work hard. Do this while prime95 is running. These tests have uncovered instability when all others seemed to show that my comp was stable. Personally, i run PC133 CAS2 Crucial memory on my Iwill KK266 at 161MHz, making my athlon 1.2 into an athlon 1.37. I think it was stable up to to an FSB speed of 164, and my above mentioned tests would fail at 165 or higher. I just ran it at 161 to be safe cause I'd never notice the extra Mhz and I love system stability.
I don't know about corrupting your hard drives' data tho. This depends on your PCI divider. I don't know if your mobo supports changing the PCI divider to 1/4. Mine is at 1/4 so my PCI bus is running at 40Mhz rather then 33Mhz, and I have no problems. This is with a 7200rpm Maxtor 20gig.