How flexible are the RP's in terms of overclocking. Obvoiusly in the PC world their are components that are literally made to be clocked but is there any evidence to suiggest that overclocking (sensibly) will damage a Pi?
Overclocking has been widely used since the first Pi four years ago. We've seen no evidence of a Pi ever being damaged.
Sure, too high an overclock may well crash the Pi, and if that crash occurs at an unlucky time, like writing to the sdcard you could get corruption.
But nothing that wouldn't be fixed by reflashing the sdcard.
Ideally back up the sdcard first (e.g. with win32diskimager), or do the tests on a new install that you don't mind reflashing, just in case.
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thanks for that reply ,so when doing this should i leave "force_turbo=0 or changge it to "1" ?
Up to you. force_turbo=1 may make the install marginally faster, but the Pi will run hotter when idle,
and it may set the warranty bit (e.g. if used in conjunction with over_voltage).