What is a safe maximum overclock on a core i7 920 do stepping with stock hsf and

If you're looking for magic number you won't find one. According to Intel spec your CPU voltage will be safe up to 1.375v and I wouldn't exceed core temps of 80deg C on stress testing such as Prime95 (blend) or LinX (full memory usage). But for the clock itself, the sky is the limit. Keep in mind exceeding Intel's specs voids your warranty and can shorten your CPU/other components life time.

You are asking for trouble by OCing the very very hot i7-9xx with stock cooler.

Get an aftermarket cooler before OCing the 920.

1.375. Missed the decimal point.

You load the processor using prime 95 small fft test at stock, use Realtemp to monotor the coretemps. If below72C, begin the overclock. Don't let it load above 75C long. Normal usage is below the load test temps.

Overclocking with a stock CPU cooler isn't a good idea.

YIKES   Thanks for catching that. 3.75 would DESTROY your CPU (if your mobo even allowed a voltage that high).

With the stock cooler, it's a question of how far you can push the chip without increasing the core voltage. And that will vary from chip to chip.