Yeah I can say 1.6V on singlestage is safe for benching 01-06 as well as of course 1m, 32m, pifast and wprime32m. Been testing for some days now and no issues so far.
For Vantage and wprime1024 I usually go down to around 1.55-1.58 just to be sure.

Also some hints collected for the single stage benchers:

- at the very beginning (first turning on ss and waiting until ~-40°C) the CPU might be very unpredictable --> don't get in a hurry then, let it idle in bios for 1-2 minutes, and then boot from the bios with previously applied settings --> should boot then
- maybe you face lock-ups with "63" "78" or "20" on the postcode --> check your rams / vccsa then --> even the cpu does 1866 or 2133 ram on air, maybe it won't under ss (unfortunatly that is one of my biggest problems)
- usually the border between boot and no boot / hard mhz wall is just 0.1 MHZ bclk speed --> it is not directly related to how high your multiplier goes
+ e.g. : 55x100 = boot and all benches | then 56x100 = freeze during windows bootscreen (typical -> best way to test is xp loading bar) | then 56x99 = boot | 59x99.5=boot | 59x99.9 = freeze | 59x99.8 = boot and most benches = absolut max without any new tweaks in bios