In rarely switched lamps, the lamp life in years will still be very long, even when the life in hours is shortened by the overvoltage
For pretty much anything else, 250V..260V is not as much of a problem. Few things come to mind though :
- It is nearing 280V, which is the limit for stuff using rectified line voltage and 400V electrolitic capacitor, so maybe something with aging capacitor won't be too happy about it (but then if the capacitor is in that bad shape, it would probably go out soon anyway)
- Few appliances use rectified line voltage and 350V electrolitic capacitor. Notably old (80s.. early 90s) Electronic ballasts. Those wouldn't be happy already with 250V. Considering their age, they wouldn't be happy at all...
- Some devices like "surge protectors" use MOVs, and in a few of them thevaristors could be rated as low as 430VDC (so ~300V assuming perfect sine wave and ideal MOVs, but could be as low as 270V if we take into account some minor line disturbances and thermal runaway of the MOVs themselfes). "surge protectors" with so low rated MOVs could be lasting quite short on such voltage