Is it safe to replace the existing micro controller with same part number but FASTER speed grade?

Ok, I have a datasheet of SC87C51 in front of me. Four speed versions are listed: 'C' (<12MHz), 'G' (<16MHz), 'P' (<24MHz) and 'Y' (<33MHz). ALL timing specifications are referenced to t(CLCL), which is clock period. In ALL timing specifications there's NO difference made for the different speed versions. E.g.: t(WHLH), which is '/RD or /WR high to ALE high', is specified as:

t(WHLH) min = t(CLCL) - 20ns, t(WHLH) max = t(CLCL) + 25ns.

So, my conclusion:

If in datasheet in specifications it's NOT distinguished between different speed versions, then there should NOT be a problem.

But have a look into datasheet of YOUR individual micro, of course!

Kai