Is it all right to run a tube right up near its maximum voltage? i.e. running a 6SN7 (max. 250V) at like 249V, give or take a few volts?

Is it all right to run a tube right up near its maximum voltage? i.e. running a 6SN7 (max. 250V) at like 249V, give or take a few volts?
I think some 6SN7 will operate at up to 300V...GT/GTB maybe? Tubes are usually very forgiving...but I wouldnt put in a rare, expensive tube at its peak. Its probably ok.

As someone once cleverly wrote, tubes don't have limits, they have guidelines. Many people run them cautiously over their limits. Not that I am suggesting you do this unless you have some specific recommendation for example.

But right on the plate voltage limit, definately, I do it all the time.

EDIT: The 6SN7-GTA for example has a design centre value of 450V. The plate will swing positive and negative from this point so it is normal for the plate to see more than that value. The absolute maximum (positive pulse) plate voltage for the GTA is actually 1.5kV. This is the true maximum.

Still though, it is common to have around 250V-350V on the plate.