Most Rev 6 68060s are marked 50MHz and there are people overclocking to 100MHz or more. I wouldn't put to much value in the 68060 clock ratings. Some SIMMs are more overclockable too. The faster timing SIMMs can usually be overclocked more but there are some with rather slow markings that will work at 50ns. It's unlikely to harm the SIMMs or CPU itself by overclocking. A more likely problem is the memory controller chip but there is usually enough tolerance to allow a mild overclock. There may be a jumper or flash memory setting to increase the wait state if the memory can't keep up. I would expect a new 60MHz oscillator only would have a 90% chance of working and give a 20% CPU speed boost. Memory becomes faster too if you don't have to add a waitstate. The custom chips and I/O may be overclocked which gives a speedup but can cause problems with motherboard memory. AGA seems to be more over clockable than ECS but 60MHz should work in both cases. It's good to monitor the temperature of the chips and provide adequate cooling. Aggressive overclocking can be tricky but mild overclocking is generally pretty safe (accelerator manufacturers did it sometimes).
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The question is what is the difference between a 50Mhz & 60Mhz version besides the markings on the chip. What I need to know is what changed on the inside as both chips seem to overclock the same. This is probably why most users go for the 50Mhz version as there are unable to get more out of their card with a 60Mhz version.
50Mhz version are also easier to find too as well as being cheaper.
What users need to be aware of is what is marked on the outside is not always what's on the inside.
